JP2014222058A - Fan rotation speed reduction detecting circuit and fan driving system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect reduction of a rotation speed of a fan with high accuracy without complicating a constitution.SOLUTION: A fan rotation speed reduction detecting circuit detects reduction of rotation speeds of a plurality of fans, and includes a signal synthesis portion, a pulse width measuring portion, a detecting portion, and a signal output portion. The signal synthesis portion receives pulse signals of which periods are changed according to the rotation speeds output from two fans among the plurality of fans, and outputs a composite pulse signal indicating the logical sum of the pulse signals. The pulse width measuring portion measures a pulse width of the composite pulse signal. The detecting portion extracts a narrowest first pulse width and a second narrowest second pulse width from the pulse widths measured by the pulse width measuring portion in a prescribed detection period, and detects the reduction of rotation speeds of two fans on the basis of the first pulse width and the second pulse width. The signal output portion outputs a rotation speed reduction signal indicating the detection of the reduction of rotation speed, when the reduction of rotation speed is detected by the detecting portion.

Description

  Embodiments described herein relate generally to a fan rotation speed decrease detection circuit and a fan drive system including the fan rotation speed decrease detection circuit.

  An apparatus having a configuration in which a component that generates heat, such as an electronic component, is provided inside a housing is provided with a plurality of cooling fan devices (hereinafter also simply referred to as fans) in order to suppress a temperature rise in the device. In this case, if the rotation speed (rotation speed) decreases due to a failure of the fan or the like, the temperature rise in the apparatus cannot be suppressed and a malfunction may occur. Therefore, in a device that requires high reliability such as an inverter device, for example, a detection circuit that constantly monitors whether or not a plurality of fans are operating normally by detecting a decrease in the number of rotations of the fan ( It is necessary to provide a fan speed reduction detection circuit.

  Generally, a fan is configured to output a pulse signal whose cycle changes in accordance with its rotational speed. Therefore, if the number of pulses of the pulse signal is counted by a counter or the like, the rotational speed can be detected. . Therefore, each pulse signal output from each fan is counted by a counter, and based on whether or not the counted value is equal to or greater than a predetermined value, whether or not the fan speed has decreased, that is, whether the fan is operating normally. Can be detected. However, in such a configuration, when the number of fans to be monitored increases, the number of necessary counters increases by the same amount, and the number of parts constituting the detection circuit increases.

  In order to eliminate the problem of increasing the number of parts, a multiplexer is provided to input the pulse signal output from each fan, and the input of the pulse signal output from each fan is time-shared by a switch or the like at regular time intervals. The structure etc. which switch to are considered. However, such a configuration requires a multiplexer having the same number of inputs as the number of fans and the same number of switches as the number of fans. In any of the configurations described above, the same number of signal lines as the number of fans are required to guide the pulse signal output from the fan to the counter. For this reason, the configuration of the apparatus is complicated, and the detection accuracy of a decrease in the rotational speed, and thus the reliability of the apparatus may be reduced.

Japanese Patent Laid-Open No. 01-136070 JP 2001-227493 A

  Accordingly, a fan speed reduction detection circuit capable of accurately detecting a fan speed reduction without complicating the configuration and a fan driving system including the fan speed reduction detection circuit are provided.

  The fan rotation speed decrease detection circuit according to the present embodiment detects a rotation speed decrease in a plurality of fans, and includes a signal synthesis unit, a pulse width measurement unit, a detection unit, and a signal output unit. The signal synthesizing unit inputs a pulse signal whose cycle changes according to the number of rotations output from any two of the plurality of fans, and outputs a synthesized pulse signal representing the logical sum of these pulse signals. The pulse width measurement unit measures the pulse width of the composite pulse signal. The detection unit extracts the narrowest first pulse width and the second narrowest second pulse width from the pulse width measured by the pulse width measurement unit within a predetermined detection period, and extracts the first pulse width. Based on the pulse width and the second pulse width, a decrease in the rotational speed of the two fans is detected. The signal output unit outputs a rotation speed reduction signal indicating that the rotation speed reduction is detected when the detection unit detects the rotation speed reduction.

The block diagram which shows 1st Embodiment and shows schematic structure of a fan rotation speed fall detection circuit Diagram showing an example in which the ON width of the pulse signal with the higher rotation speed appears in the composite pulse signal Diagram showing an example in which the ON width of the pulse signal with the lower rotation speed appears in the composite pulse signal The figure which shows each pulse signal in the 1st case The figure which shows each pulse signal in the 2nd case The figure which shows each pulse signal in the 3rd case The figure which shows each pulse signal in the 4th case The figure showing the 1st ON width in each case, the 2nd ON width, and ratio p (the 1) A diagram showing the first ON width, the second ON width and the ratio p in each case (No. 2) The figure showing the 1st ON width in each case, the 2nd ON width and ratio p (the 3) The figure showing the 1st ON width in each case, the 2nd ON width, and ratio p (the 4) The block diagram which shows 2nd Embodiment and shows schematic structure of a fan drive system

Hereinafter, a plurality of embodiments will be described with reference to the drawings. In each embodiment, substantially the same components are denoted by the same reference numerals and description thereof is omitted.
(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
A fan rotation speed decrease detection circuit 1 (hereinafter also referred to as a detection circuit 1) shown in FIG. 1 includes, for example, a plurality of fans provided in an inverter device (in FIG. 1, reference numerals 2 and 3 are attached and only two are shown). A decrease in the rotational speed (rotational speed) at is detected. The plurality of fans are divided into two groups. Then, the detection circuit 1 detects a decrease in the rotational speed for each group. In FIG. 1, constituent parts for detecting a decrease in the rotational speed of the fans 2 and 3 constituting one group are extracted and shown. Further, the two fans constituting the same group have the same rated rotational speed.

  The fans 2 and 3 are driven based on a drive signal given from a drive unit (not shown). The fans 2 and 3 output pulse signals Pa and Pb whose periods change according to the rotation speed. Further, the pulse signals Pa and Pb are fixed to the H level (level representing positive logic) when the fans 2 and 3 are locked (= when the rotational speed is zero).

  The duty of the pulse signals Pa and Pb (in this case, the ON duty) is designed to be 50%, but actually varies within a range of 40 to 60% (there is variation). As shown in FIG. 1, the output circuit that outputs the pulse signals Pa and Pb in the fans 2 and 3 is an open collector output by an NPN transistor. The pulse signals Pa and Pb output from the fans 2 and 3 are given to the detection circuit 1 through the signal lines 4 and 5.

  The detection circuit 1 includes a logic circuit 6 (corresponding to a signal synthesis unit) and a control circuit 7. The logic circuit 6 is a wired OR that obtains a combined pulse signal Pc representing the logical sum of the pulse signals Pa and Pb by connecting the signal lines 4 and 5. The composite pulse signal Pc output from the logic circuit 6 is given to the control circuit 7.

  The control circuit 7 is mainly composed of a microcomputer. The control circuit 7 realizes functions as a pulse width measurement unit 8, a detection unit 9, and a signal output unit 10 by executing a predetermined program. The pulse width measurement unit 8 measures the pulse width of the composite pulse signal Pc supplied from the logic circuit 6 using a counter (timer) provided in the control circuit 7. The pulse width referred to here is a width when the composite pulse signal Pc is at the H level (level representing positive logic), and is also referred to as an ON width in the following description. Data representing the measurement result of the ON width by the pulse width measurement unit 8 is given to the detection unit 9.

  The detection unit 9 includes a first ON width W1 (corresponding to the first pulse width) having the narrowest width among the ON widths measured by the pulse width measurement unit 8 within a predetermined detection period (for example, 30 minutes). The second narrowest second ON width W2 (corresponding to the second pulse width) is extracted, and a decrease in the rotational speed of the two fans 2 and 3 is detected based on the ON widths W1 and W2 (details are given below) Will be described later). When the detection unit 9 detects a decrease in the rotational speed, the signal output unit 10 outputs a rotational speed decrease signal Sa indicating that the rotational speed decrease has been detected.

  The extraction of the second ON width W2 by the detection unit 9 needs attention in the following points. That is, as described above, the pulse width measurement unit 8 measures the ON width of the composite pulse signal Pc using a counter. Therefore, depending on the resolution of the counter, even if the ON width is actually the same, the measured value may be slightly different every time it is measured. Then, among the measured values obtained by measuring the same ON width having the narrowest width, the smallest value is extracted as the first ON width W1, and the second smallest value is extracted as the second ON width W2. There is a possibility that the ON width having a narrow width may not be extracted as the second ON width W2.

Therefore, after extracting the first ON width W1, the ON width corresponding to the condition of the following expression (1) is excluded from the extraction targets of the second ON width W2 from the remaining ON width W. However, β is for compensating an error in measurement by the pulse width measuring unit 8 and is set to a value of about several percent.
W / W1 <1 + β% (1)
As shown in the above equation (1), those having a ratio close to “1” with the first ON width W1, that is, those having a relatively small difference from the first ON width W1, are excluded from the extraction targets of the second ON width W2. Then, it is possible to extract the ON width that should be originally extracted as the second ON width W2.

  The detection operation of the rotation speed reduction by the detection unit 9 is repeatedly performed every detection period after the driving of the fans 2 and 3 is started and the rotation state thereof is stabilized. In addition, when the driving of the fans 2 and 3 is stopped, the execution of the operation for detecting the rotation speed reduction by the detection unit 9 is also stopped. The reason for this is that when the detection operation is continued after the driving of the fans 2 and 3 is stopped, a decrease in the rotational speed that occurs regardless of deterioration or failure (a decrease in the rotational speed that always occurs after the driving is stopped) is detected. This is because false detection occurs. As described above, the detection circuit 1 detects a decrease in the rotational speed due to deterioration or failure of the fans 2 and 3.

  The detection unit 9 detects the fan lock of the two fans 2 and 3 based on the combined pulse signal Pc. Specifically, the detection unit 9 determines that at least one of the two fans 2 and 3 is fan-locked when the combined pulse signal Pc is fixed at the H level for a predetermined period. When the detection unit 9 detects fan lock, the signal output unit 10 outputs a failure detection signal Sb indicating that fan lock has been detected.

Next, a method for detecting a decrease in the rotational speed by the detection unit 9 will be described in detail.
If the ON widths of the pulse signals Pa and Pb outputted from the fans 2 and 3 are known, the ON widths of the pulse signals Pa and Pb at the rated rotation are compared with the ON widths (specification values) of the fan 2 3 can be determined. However, since the pulse signals Pa and Pb are not input to the detection circuit 1, the ON widths of the pulse signals Pa and Pb cannot be directly measured. Instead, a combined pulse signal Pc representing the logical sum of the pulse signals Pa and Pb is input to the detection circuit 1. Therefore, in the present embodiment, a decrease in the rotational speed of the fans 2 and 3 is determined based on the ON width of the composite pulse signal Pc.

  As described above, the fans 2 and 3 are fans having the same rated rotational speed. However, when actually operating, the fans 2 and 3 do not always rotate at the rated rotational speed. Are almost never matched. That is, the pulse signals Pa and Pb output from the fans 2 and 3 having the same rated rotational speed are completely in the cycle (ON width) even when the fans 2 and 3 are operating normally. It will be slightly different without matching. The pulse signals Pa and Pb are not synchronized because they are generated in the fans 2 and 3 at their own timing. For this reason, the relationship between the pulse signals Pa and Pb changes as time elapses. When the relationship between the pulse signals Pa and Pb satisfies the following conditions, the ON widths of the pulse signals Pa and Pb appear in the combined pulse signal Pc.

  In this case, the rotation speed (rotation speed) of the fan 3 is slower than the rotation speed (rotation speed) of the fan 2, that is, the ON width of the pulse signal Pb is larger than the ON width of the pulse signal Pa. Is assumed to be wider.

“1” Condition in which ON width of pulse signal with higher rotation speed appears in composite pulse signal As shown in FIG. 2, ON width of pulse signal Pa is OFF width of pulse signal Pb (level representing negative logic = L level) Is smaller than the width of the pulse signal Pa, the ON width of the pulse signal Pa appears in the composite pulse signal Pc. That is, the condition that the ON width aon of the pulse signal Pa appears in the composite pulse signal Pc can be expressed as the following equation (2). However, the duty of the pulse signal Pb is Db, and the OFF width of the pulse signal Pb is boff.
aon <(bon / Db) −bon = boff (2)

“2” Conditions in which the ON width of the pulse signal with the slower rotation speed appears in the composite pulse signal As shown in FIG. 3, when the rise and fall of the pulse signal Pb exist in the OFF width period of the pulse signal Pa, The ON width of the pulse signal Pb appears in the synthesized pulse signal Pc. That is, the condition that the ON width bon of the pulse signal Pb appears in the combined pulse signal Pc can be expressed as the following equation (3). However, the duty of the pulse signal Pa is Da. N is 0 or a positive integer.
aon + n × (aon / Da) <bon <(n + 2) × (aon / Da) −aon (3)

  The ON widths of the pulse signals Pa and Pb appearing in the composite pulse signal Pc under the above-described conditions are the narrowest and the second-widest of the ON widths of the composite pulse signal Pc measured within the detection period. It will be narrow. However, when the above conditions are not satisfied, the ON widths of the pulse signals Pa and Pb cannot be obtained from the first ON width W1 and the second ON width W2. In view of this, the relationship between the ON widths W1 and W2 and the ON widths of the pulse signals Pa and Pb when the pulse signals Pa and Pb have a relationship will be described below with a specific example.

“1” First Case When the pulse signals Pa and Pb have the relationship as shown in FIG. 4, the ON width of the pulse signal Pa does not appear in the combined pulse signal Pc. This is because, at this time, the ON width aon of the pulse signal Pa and the ON width bon of the pulse signal Pb have the relationship shown in the following equation (4) and do not satisfy the condition of the above-described equation (2). is there. Note that equation (5) is a modification of equation (4).
aon> (bon / Db) -bon (4)
bon <(a × Db) / (1-Db) (5)

  In this case, the ON width of the combined pulse signal Pc becomes the narrowest when the ON width period of the pulse signal Pa is completely included in the ON width period of the pulse signal Pb. Accordingly, the first ON width W1 is “bon”. Further, the ON width of the combined pulse signal Pc is the second narrowest when the ON width period of the pulse signal Pa slightly protrudes from the ON width period of the pulse signal Pb. Therefore, the second ON width W2 is “bon + α” (where α is almost zero and the length of the slightly protruding portion described above).

“2” Second Case When the ON width of the pulse signal Pb becomes wider than that in the first case and the pulse signals Pa and Pb have the relationship shown in FIG. 5, the ON width of the pulse signals Pa and Pb becomes the combined pulse signal. Appears at Pc. Because, at this time, the ON width aon of the pulse signal Pa and the ON width bon of the pulse signal Pb have the relationship shown in the following formula (6), and the conditions of the formulas (2) and (3) described above are satisfied. Because it satisfies.
(A * Db) / (1-Db) <bon <(2 * aon / Da) -aon (6)

  In this case, the ON width of the combined pulse signal Pc is the narrowest when the ON width period of the pulse signal Pa overlaps the OFF width period of the pulse signal Pb. Accordingly, the first ON width is “aon”. Further, the ON width of the combined pulse signal Pc becomes the second narrowest when the rising and falling edges of the pulse signal Pb are present during the OFF width period of the pulse signal Pa. Therefore, the second ON width W2 is “bon”.

“3” Third Case When the ON width of the pulse signal Pb becomes wider than that in the second case, and the pulse signals Pa and Pb have the relationship shown in FIG. 6, the ON width aon of the pulse signal Pa becomes the combined pulse signal Pc. However, the ON width of the pulse signal Pb does not appear in the synthesized pulse signal Pc. This is because, at this time, the ON width aon of the pulse signal Pa and the ON width bon of the pulse signal Pb have the relationship shown in the following equation (7). That is, although the condition of the expression (2) described above is satisfied, the condition of the expression (3) is not satisfied.
(2 × aon / Da) −aon <bon <a + (a / Da) (7)

  In this case, the ON width of the combined pulse signal Pc is the narrowest when the ON width period of the pulse signal Pa overlaps the OFF width period of the pulse signal Pb. Accordingly, the first ON width is “aon”. Further, the ON width of the combined pulse signal Pc is the second narrowest when the rising and falling edges of the pulse signal Pb are present in the ON width period of the pulse signal Pa. Therefore, the second ON width W2 is “aon + (aon / Da)”.

“4” Fourth Case When the ON width of the pulse signal Pb becomes wider than that in the third case, and the pulse signals Pa and Pb have the relationship shown in FIG. 7, the ON width of the pulse signals Pa and Pb becomes the combined pulse signal. Appears at Pc. Because, at this time, the ON width aon of the pulse signal Pa and the ON width bon of the pulse signal Pb have the relationship shown in the following formula (8), and the conditions of the formulas (2) and (3) described above are satisfied. Because it satisfies.
aon + (aon / Da) <bon <(3 × aon / Da) −aon (8)

  In this case, the ON width of the combined pulse signal Pc is the narrowest when the ON width period of the pulse signal Pa overlaps the OFF width period of the pulse signal Pb. Accordingly, the first ON width is “aon”. Further, the ON width of the combined pulse signal Pc becomes the second narrowest when the rising and falling edges of the pulse signal Pb are present during the OFF width period of the pulse signal Pa. Therefore, the second ON width W2 is “bon”.

  In the description of each case described above, the point that the duty of the pulse signals Pa and Pb varies is not considered. Therefore, the cases shown in FIGS. 8 to 11 are as shown in FIGS. 8 to 11 when the variations (40% to 60%) of the duty of the pulse signals Pa and Pb are taken into consideration. 8 to 11 show the first ON width W1, the second ON width W2, and the ratio p (= W2 / W1) of the first ON width W1 and the second ON width W2 in each case.

FIG. 8 shows a case where the duty of the pulse signals Pa and Pb is 50% or more (Da = 50 to 60%, Db = 50 to 60%). The relationship between the pulse signals Pa and Pb in the first case of FIG. 8 can be expressed as the following equation (9). However, the duty Db is 60%.
bon <3 × (aon / 2) (9)
In this case, the ratio p (= (b + α) / b) is a value close to 1 (p≈1).

The relationship between the pulse signals Pa and Pb in the second case of FIG. 8 can be expressed as the following equation (10). However, the duties Da and Db are both 50%.
aon <bon <3 × aon (10)
In this case, the ratio p (= b / a) is a value between 1 and 3 (1 <b / a <3).

The relationship between the pulse signals Pa and Pb in the third case of FIG. 8 can be expressed as the following equation (11). However, the duty Da is set to 60%.
(7/3) × aon <bon <(8/3) × aon (11)
In this case, the ratio p (= (aon + (aon / Da)) / aon) is larger than 8/3 (1+ (1 / Da)> 8/3).

The relationship between the pulse signals Pa and Pb in the fourth case of FIG. 8 can be expressed as the following equation (12). However, the duty Da is set to 60%.
(8/3) × aon <bon <4 × aon (12)
In this case, the ratio p (= b / a) is larger than 8/3 (b / a> 8/3).

  FIG. 9 shows the case where the duty of the pulse signal Pa is 50% or more and the duty of the pulse signal Pb is 50% or less (Da = 50-60%, Db = 40-50%). In this case, the first case does not exist. This is because if the duty Db is 40% in the above equation (5), the equation will not hold. The relationship between the pulse signals Pa and Pb and the ratio p in the second to fourth cases in FIG. 9 are the same as those in the second to fourth cases in FIG.

  FIG. 10 shows the case where the duty of the pulse signal Pa is 50% or less and the duty of the pulse signal Pb is 50% or more (Da = 40 to 50%, Db = 50 to 60%). In this case, the third case does not exist. This is because if the duty Da is set to 40% in the equation (7), the equation is not satisfied. The relationship between the pulse signals Pa and Pb and the ratio p in the first case of FIG. 10 are the same as those in the first case of FIG.

The relationship between the pulse signals Pa and Pb in the second case of FIG. 10 can be expressed as the following equation (13). However, the duty Da is 40% and the duty Db is 50%.
aon <bon <4 × aon (13)
In this case, the ratio p (= b / a) is a value between 1 and 4 (1 <b / a <4).

The relationship between the pulse signals Pa and Pb in the fourth case of FIG. 10 can be expressed as the following equation (14). However, the duty Da is set to 50%.
3 × aon <bon <5 × aon (14)
In this case, the ratio p (= b / a) is larger than 3 (b / a> 3).

  FIG. 11 shows a case where the duty of the pulse signals Pa and Pb is 50% or less (Da = 40 to 50%, Db = 40 to 50%). In this case, the first case does not exist. This is because if the duty Db is 40% in the above equation (5), the equation will not hold. In this case, the third case does not exist. This is because if the duty Da is set to 40% in the equation (7), the equation is not satisfied. The relation between the pulse signals Pa and Pb and the ratio p in the second case and the fourth case in FIG. 11 are the same as those in the second case and the fourth case in FIG.

  Now, when the rotation speed is lowered due to clogging or deterioration in the fans 2 and 3, the ON widths and cycles of the output pulse signals Pa and Pb become longer than normal. However, it is unlikely that the fans 2 and 3 are clogged and deteriorated at the same time. In many cases, when one of the fans 2 and 3 is clogged or deteriorated, it can be considered that the other is still normal. That is, when the rotation speed of any one of the fans 2 and 3 is reduced, the other rotation speed is considered to substantially match the rated rotation speed. Therefore, when the ratio of the ON widths of the fans 2 and 3 (= longer ON width / shorter ON width) is close to 1, it is considered that there is a low possibility that the rotational speed is reduced. It is considered that the larger the value is, the higher the possibility that the rotational speed is reduced.

  As described above, in the second case and the fourth case, the ratio p between the first ON width W1 and the second ON width W2 of the composite pulse signal Pc is the ratio of the ON widths of the fans 2 and 3 (b / a). Matches. Therefore, in the second case and the fourth case, it is possible to determine whether the rotational speed is reduced based on the value of the ratio p. In the second case, the value of p is a value between 1 and 4 (1 <p <4). In the fourth case, the value of p is larger than 8/3 (p> 8/3).

  On the other hand, in the first case and the third case, the ratios p are “1+ (1 / Da)” and “(b + α) / b”, respectively, which do not match the ON width ratio of the fans 2 and 3. However, in the first case, as shown in FIG. 5, the ON width bon of the fan 3 is slightly longer than the ON width aon of the fan 2. In other words, in the case of the first case, it is considered that it is not necessary to determine that the rotational speed has decreased. In this case, the value of p is approximately 1 (p≈1). On the other hand, in the third case, as shown in FIG. 7, the ON width bon of the fan 3 is sufficiently longer than the ON width aon of the fan 2. In other words, in the case of the third case, it is considered necessary to determine that the rotational speed has decreased. In this case, the value of p is larger than 8/3 (p> 8/3).

  Based on this, in the present embodiment, when the value of p exceeds 7/3 (corresponding to the determination threshold), it is determined that the rotational speed of one of the two fans 2 and 3 has decreased. , 7/3 or less, the rotational speed reduction determination described later is performed. If it does in this way, in the case of the 1st case and the 2nd case, rotation speed fall judgment will be performed. In the third case and the fourth case, since the value of p is larger than 8/3, it is always determined that the rotational speed is reduced. The determination threshold can be changed as appropriate as long as it is a value smaller than 8/3.

The rotational speed reduction determination is performed based on the following equation (15). However, the ON widths of the pulse signals Pa and Pb output during rated rotation of the fans 2 and 3 are set to Wd.
W2 ≧ Wd × (1 / X%) (15)

  As shown in the above equation (15), the second ON width W2 is a value that is “1 / X%” times the ON width Wd of the pulse signals Pa and Pb output during rated rotation of the fans 2 and 3 (decrease judgment value). If it is above, it will be judged that one rotation number among the fans 2 and 3 fell. If it does in this way, when rotation speed will fall to X% at the time of rating, it will be judged that rotation speed fell. On the other hand, if the second ON width W2 is less than the decrease determination value, it is not determined that the rotational speed has decreased. Note that the decrease determination value, that is, the value of X% can be appropriately changed as long as it is larger than the reciprocal of the determination threshold (for example, 3 / 7≈42.86%).

As described above, according to the present embodiment, the following effects can be obtained.
The detection circuit 1 divides a plurality of fans into two groups, and detects a decrease in the rotation speed for each group. The detection circuit 1 calculates the logical sum of the pulse signals Pa and Pb output from the two fans 2 and 3. A logic circuit 6 that outputs a synthesized pulse signal Pc to be expressed and a control circuit 7 that detects a decrease in the rotational speed of the fans 2 and 3 based on the synthesized pulse signal Pc are provided. The control circuit 7 measures the ON width of the composite pulse signal Pc and extracts the narrowest first ON width W1 and the second narrowest second ON width W2 from the ON widths measured during the detection period. Then, based on the ON widths W1 and W2 and their ratio p, a decrease in the rotational speed of the two fans 2 and 3 is detected.

  According to such a configuration, the number of counters, switches, and signal lines for guiding the pulse signal from the fan to the counter, which were conventionally required by the same number as the number of fans, are reduced to half. A decrease in the rotational speed of the fans 2 and 3 can be detected. Therefore, according to the present embodiment, it is possible to accurately detect a decrease in the rotational speed of a plurality of fans without complicating the configuration. Further, since the logic circuit 6 for obtaining the combined pulse signal Pc representing the logical sum of the pulse signals Pa and Pb is a wired OR that can be configured simply by connecting the signal lines 4 and 5, the configuration is further simplified. The effect is obtained. In addition, since the number of signal lines for guiding the pulse signal to the counter is halved, an effect of improving the reliability of the rotation speed reduction detection can be obtained.

(Second Embodiment)
Hereinafter, a second embodiment will be described with reference to FIG.
As shown in FIG. 12, the fan drive system 21 includes the detection circuit 1 of the first embodiment, the fans 2 and 3, the fan drive unit 22, and the fan control unit 23 in which the detection circuit 1 detects a decrease in the rotational speed. I have.

  The fan drive unit 22 drives the fans 2 and 3 by outputting a drive signal to the fans 2 and 3 in accordance with a drive command given from the fan control unit 23. The fan control unit 23 controls the operation of the fan drive unit 22. The fan control unit 23 is supplied with a rotation speed reduction signal Sa and a failure detection signal Sb output from the signal output unit 10 of the detection circuit 1. The detection circuit 1 outputs data (not shown) representing the ON width Y of the composite pulse signal Pc to the fan control unit 23.

  When the rotation speed reduction signal Sa is given, the fan control unit 23 specifies which rotation speed of the fans 2 and 3 has decreased as follows. That is, when the rotation speed reduction signal Sa is given, the fan control unit 23 controls the operation of the fan drive unit 22 so as to stop driving one of the fans 2 and 3, for example, the fan 3. In this case, since only the fan 2 which is the other fan is driven, the synthesized pulse signal Pc obtained in the detection circuit 1 is the pulse signal Pa itself.

In such a state, the fan control unit 23 acquires the ON width Y of the composite pulse signal Pc from the data given from the detection circuit 1. And the fan control part 23 calculates | requires the rotation speed m of the fan 2 based on following (16). However, z is the number of pulses output per rotation and is determined by the specifications of the fans 2 and 3. D is the specification value (50%) of the duty (ON duty) of the pulse signals Pa and Pb.
m [min−1] = 60 / (z · (Y / D)) (16)

  The fan control unit 23 compares the rotational speed m of the fan 2 obtained based on the above equation (16) with the rotational speed (rated rotational speed) at the rated rotational speed of the fan 2, and the rotational speed m is the rated rotational speed. If it is lower than the predetermined value, the fan 2 is identified as having a reduced rotational speed. Further, the fan control unit 23 specifies that the rotation speed is reduced in the fan 3 when the rotation speed m is not lower than the rated rotation speed by a predetermined value or more. And the fan control part 23 performs the predetermined | prescribed alerting | reporting operation | movement which alert | reports to the user that the rotation speed of the fan specified as mentioned above has fallen.

  When the failure detection signal Sb is given, the fan control unit 23 specifies which of the fans 2 and 3 has a fan lock as follows. In other words, when the failure detection signal Sb is given, the fan control unit 23 controls the operation of the fan drive unit 22 so as to stop driving one of the fans 2 and 3, for example, the fan 3. At this time, when the synthesized pulse signal Pc changes in a pulse shape from the state where it is fixed at the H level, the fan control unit 23 specifies that the fan 3 is fan-locked.

  Further, when the state in which the composite pulse signal Pc is fixed to the H level continues, the fan control unit 23 specifies that the fan lock is generated in the fan 2 which is the other fan. Furthermore, in this case, the fan 3 may be fan-locked. Therefore, the fan control unit 23 controls the operation of the fan driving unit 22 so as to stop the driving of the fan 2 and drive the fan 3. In this state, when the composite pulse signal Pc is pulsed, the fan control unit 23 determines that the fan 3 is not fan-locked. On the other hand, when the composite pulse signal Pc is fixed to the H level, the fan control unit 23 determines that the fan 3 is also locked in the fan 3. And the fan control part 23 performs the predetermined | prescribed alerting | reporting operation | movement which alert | reports that the fan lock | rock has generate | occur | produced in the fan specified as mentioned above with respect to a user.

  The fan control unit 23 controls the operation of the fan drive unit 22 so that the two fans 2 and 3 are driven one by one when the fan drive system 21 is activated. Then, the fan control unit 23 confirms whether or not there is a decrease in the rotational speed and fan lock in the fans 2 and 3 based on the ON width Y of the combined pulse signal Pc in a state where the fans 2 and 3 are driven. In addition, what is necessary is just to employ | adopt the method similar to the method mentioned above about the rotation speed fall and the presence or absence of a fan lock. Then, when it is confirmed that neither the rotation speed reduction nor the fan lock occurs in any of the fans 2 and 3, the fan control unit 23 shifts to a normal operation state. In addition, when it is confirmed that at least one of the fans 2 and 3 has a decrease in the rotational speed or fan lock, the fan control unit 23 performs a predetermined notification operation to notify the user of such an abnormality. Run.

  As described above, in the fan drive system 21 of the present embodiment, when the detection circuit 1 detects that the rotation speed is reduced or the fan lock has occurred in any of the fans 2 and 3, One drive is stopped, and the other rotation speed of the fans 2 and 3 is detected based on the ON width Y of the composite pulse signal Pc output in that state, and the detected value and the rated rotation speed of the fans 2 and 3 are detected. In this way, the fan in which the rotational speed drop or fan lock has occurred is identified. In this way, the user can know which fan among the plurality of fans has deteriorated or failed, and the convenience of the user when performing fan maintenance is improved.

  In the fan drive system 21, two fans 2 and 3 are driven one by one at the time of startup, and the fan 2 is based on the ON width Y of the composite pulse signal Pc in a state where the fans 2 and 3 are driven. 3 is confirmed whether there is a decrease in the rotational speed and whether there is a fan lock. When it is confirmed that neither the rotation speed reduction nor the fan lock has occurred in any of the fans 2 and 3, the normal operation state is entered, and at least one of the fans 2 and 3 has the rotation speed reduction or the fan lock. When it is confirmed that the occurrence has occurred, such an abnormality is notified to the user. According to such a configuration, the normal operation is performed only when it is confirmed that there is no abnormality in the plurality of fans at the time of starting the system, so that the safety and reliability of the system are further improved. can get.

(Other embodiments)
As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention.

  The output stage (output circuit) of the fans 2 and 3 may be an open drain output, or may be another system. However, when other systems are used as the output stages of the fans 2 and 3, it is necessary to provide an OR gate (logic circuit) instead of a wired OR as the signal synthesis unit. The signal synthesis unit may be any unit that outputs a synthesized pulse signal Pc representing the logical sum of the pulse signals output from the two fans 2 and 3. Therefore, the signal synthesis unit can be configured by a logic circuit including OR or AND. When a logic circuit including AND is employed as the signal synthesis unit, a configuration in which an AND gate and an inversion gate are combined so that a synthesized pulse signal Pc representing a logical sum of two pulse signals can be obtained.

  The detection unit 9 is an exclusion determination that is set to be equal to or less than the ON widths (specification values) of the pulse signals Pa and Pb output by the two fans 2 and 3 during rated rotation, among the ON widths measured by the pulse width measurement unit 8. You may make it exclude ON width less than a value from the object extracted as 1st ON width W1 and 2nd ON width W2. In this way, it is possible to prevent the occurrence of erroneous detection due to the influence of noise or the like superimposed on the signal lines 4 and 5, for example.

  When the fans 2 and 3 are locked (= when the rotation speed is zero), the specification is such that the pulse signals Pa and Pb are fixed to L level (a level representing negative logic). It should be changed as follows. That is, the detection unit 9 determines that at least one of the two fans 2 and 3 is in a state where the combined pulse signal Pc is fixed at the L level or the ON width of the combined pulse signal Pc is constant for a predetermined period. It may be determined that the fan is locked. For example, the following method can be used to determine whether or not the ON width of the composite pulse signal Pc is constant. That is, the detection unit 9 extracts the widest ON width (Wmax) and the narrowest ON width (Wmin) among the ON widths of the composite pulse signal Pc measured by the pulse width measurement unit 8 within a predetermined period. If the ratio (= Wmax / Wmin) is less than a predetermined value (for example, 2), it is determined that the ON width is constant. Note that the predetermined value is not limited to 2, and can be appropriately changed as long as the value is larger than 1.

  When the specifications are such that the pulse signals Pa and Pb are fixed at the L level when the fans 2 and 3 are locked, the fan control unit 23 determines in which of the fans 2 and 3 the fan lock has occurred as follows. Should be specified. That is, when the failure detection signal Sb is given, the fan control unit 23 specifies that fan lock has occurred in both the fans 2 and 3 when the composite pulse signal Pc is fixed at the L level. . Further, when the failure detection signal Sb is given, the fan control unit 23 stops driving one of the fans 2 and 3 (for example, the fan 3) when the ON width of the combined pulse signal Pc is constant. Thus, the operation of the fan drive unit 22 is controlled. At this time, if there is no change in the composite pulse signal Pc (the ON width remains constant), the fan control unit 23 specifies that fan lock has occurred in one of the fans (fan 3). Further, when the composite pulse signal Pc changes to a state where it is fixed at the L level, the fan control unit 23 specifies that the fan lock has occurred in the other fan (fan 2).

The detection method of the rotational speed drop in each of the above embodiments is intended for two fans having the same rated rotational speed, but may be targeted for two fans having different rated rotational speeds. However, in that case, it is necessary to appropriately correct the conditional expression for making each determination so as to reflect the difference in the rated rotational speed of the two fans.
These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the drawing, 1 is a fan rotation speed decrease detection circuit, 2 and 3 are fans, 6 is a logic circuit (signal synthesis unit), 8 is a pulse width measurement unit, 9 is a detection unit, 10 is a signal output unit, and 21 is fan drive. The system, 22 is a fan drive unit, and 23 is a fan control unit.

Claims (7)

A fan rotation speed decrease detection circuit for detecting a decrease in the rotation speed of a plurality of fans,
A signal synthesizer that inputs a pulse signal whose cycle changes according to the number of rotations output from any two of the plurality of fans, and outputs a synthesized pulse signal that represents a logical sum of the pulse signals;
A pulse width measuring unit for measuring the pulse width of the combined pulse signal;
The narrowest first pulse width and the second narrowest second pulse width are extracted from the pulse widths measured by the pulse width measuring unit within a predetermined detection period, and these first pulses are extracted. A detection unit for detecting a decrease in the rotational speed of the two fans based on the width and the second pulse width;
A signal output unit that outputs a rotation speed reduction signal indicating that a rotation speed reduction is detected when the detection unit detects a rotation speed reduction;
A fan rotation speed decrease detection circuit comprising: The detector is
Determining a ratio of the first pulse width and the second pulse width;
If the ratio exceeds the determination threshold, it is determined that the rotational speed of at least one of the two fans has decreased,
When the ratio is equal to or less than the determination threshold, the second pulse width is equal to or greater than the decrease determination value set to a value longer than the pulse width of the pulse signal output by the two fans during rated rotation. 2. The fan rotation speed decrease detection circuit according to claim 1, wherein it is determined that the rotation speed of at least one of the two fans has decreased.   The detection unit has a pulse width less than an exclusion determination value set to be equal to or less than a pulse width of a pulse signal output by the two fans during rated rotation out of the pulse width measured by the pulse width measurement unit. 3. The fan rotation speed decrease detection circuit according to claim 1, wherein the fan rotation speed drop detection circuit is excluded from a target to be extracted as one pulse width and the second pulse width. 4. The detection unit determines that at least one of the two fans is fan-locked when a state in which the composite pulse signal is fixed at a level representing positive logic continues for a predetermined period of time,
4. The signal output unit according to claim 1, wherein when the fan lock is detected by the detection unit, the signal output unit outputs a failure detection signal indicating that the fan lock has been detected. 5. Fan speed drop detection circuit. When the state where the composite pulse signal is fixed to a level representing negative logic or the state where the pulse width of the composite pulse signal is constant is continued for a predetermined period, at least one of the two fans. Judge that one of them is fan-locked
5. The signal output unit according to claim 1, wherein when the fan lock is detected by the detection unit, the signal output unit outputs a failure detection signal indicating that the fan lock has been detected. 6. Fan speed drop detection circuit. Two fans whose rotation speed reduction is detected by the fan rotation speed reduction detection circuit according to any one of claims 1 to 5, a fan driving unit that drives the two fans, and a fan driving unit A fan drive system including a fan control unit for controlling operation,
The signal output unit outputs the rotation speed reduction signal to the fan control unit,
When the rotation speed reduction signal is input, the fan control unit controls the operation of the fan driving unit to stop driving one of the two fans, and outputs the signal from the signal synthesis unit in that state. And detecting the rotational speed of the other of the two fans based on the synthesized pulse signal, and comparing the detected value and the rated rotational speed of the fan, thereby identifying the fan whose rotational speed has decreased. And fan drive system.   The fan control unit controls the operation of the fan driving unit so as to drive the two fans one by one at the time of system startup, and the synthesis output from the signal synthesizing unit while driving each fan. Based on the pulse signal, it is confirmed whether or not the rotational speeds of the two fans have decreased. If not, the normal operation state is entered. The fan drive system according to claim 6, wherein a notification operation for notifying the user of the decrease is executed.

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