JPH079105Y2 - Automatic range circuit - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to an auto-ranging circuit, and more specifically, when measuring the level of a signal under measurement with a measuring instrument, etc. The present invention relates to an autoranging circuit whose range is automatically switched.

[Conventional technology]

When measuring the voltage level or current level of a signal under measurement with a measuring instrument that has several measurement ranges, depending on the measuring instrument, the range can be automatically switched depending on the magnitude of the input signal. Some have a circuit.

Conventionally, this kind of auto-ranging circuit is composed of a shift register or the like. That is, when a range up signal or a range down signal is input to the clock input terminal, the output is shifted accordingly and range switching is performed.

[Problems to be solved by the device]

However, when the shift register has, for example, 4 bits, only four range switching stages can be taken. Therefore, in order to increase the number, it is necessary to separately add a shift register, which complicates the circuit configuration and also increases the price.

Further, according to Japanese Patent Application Laid-Open No. 58-173910, there is provided amplification means, switching means for switching the amplification degree of the amplification means, and range control means, and when the output of the amplification means exceeds or falls below a predetermined threshold value. , An amplification circuit in which the amplification degree of the amplification means is switched step by step. In this prior art example, the range control means is composed of two flip-flop circuits and logic elements such as three NOR circuits which theoretically combine the output signals of the circuits to form a range signal. As in the case of the shift register, when the number of range stages to be switched increases, the number of elements such as flip-flop circuits significantly increases, the circuit configuration becomes complicated, and the cost inevitably increases.

The present invention has been made to solve the above-mentioned conventional drawbacks, and its purpose is to have a simple configuration including a counter circuit, a flip-flop circuit, and the like, and to easily and arbitrarily set the number of stages of the range to be switched according to the measurement function. It is to provide an autoranging circuit that can be set to.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention provides a level of a signal under measurement applied to an A / D converter 3 from a signal source via a range setting circuit 2 and a signal under measurement capable of being digitally converted by the A / D converter 3. Is compared with the allowable upper limit level or the allowable lower limit level, and is output from the A / D converter 3 when the level of the input measured signal exceeds the upper limit level or does not reach the lower limit level. First and second gate circuits 6 and 8 for selectively passing the continuation signal as a clock signal for counting,
A flip-flop circuit 7 for receiving a continuation signal generated when the upper limit level is exceeded and outputting an up counting mode signal, and for receiving a continuation signal generated when the lower limit level is not reached and outputting a down counting mode signal; The up-count mode signal from the flip-flop circuit 7 up-counts the continuation signal generated when the upper limit level is exceeded, and the down-count mode signal from the flip-flop circuit 7 raises the lower limit level. An up / down counter 10 that down-counts a continuous signal and sends a range up or range down switching signal to the range setting circuit 2, and a signal corresponding to a desired range is given to the up / down counter 10 to set the range. A preset circuit capable of arbitrarily setting the range of the circuit 2 13, the first and second gate circuits 6 and 8 and the up-down counter 10 are respectively interposed between the output sides, and the output of the up-down counter 10 turns on the first gate passage of the continuation signal. It is characterized by including a NAND gate circuit 11 for controlling ON / OFF and an OR gate circuit 12 for controlling ON / OFF of the second gate passage of the intermittent signal.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the accompanying drawings. FIG. 1 shows an embodiment in which the auto-ranging circuit according to the present invention is applied to a digital measuring instrument.

According to this, the signal under measurement emitted from the signal source 1 is input to the A / D converter 3 via the range setting circuit 2, converted into a digital signal, and then sent to the measurement unit 4.

The auto-ranging circuit 5 according to the present invention, when the level of the signal under measurement input to the range setting circuit 2 exceeds the setting range or does not reach the setting range,
It receives a range over signal or a range under signal emitted from the D converter 3, forms a range up signal or a range down signal for setting range switching, and sends it to the range setting circuit 2.

Next, the configuration of the auto range circuit 5 will be described. First, the range-over signal sent from the A / D converter 3 is reset through, for example, one input end of the AND circuit 6 and the D flip-flop circuit (hereinafter referred to as "D-FF") 7 via the terminal T1. Applied to terminal R. Similarly, the range under signal sent from the A / D converter 3 is supplied to the one input terminal of the AND circuit 8 via the terminal T2,
It is added to the set terminal S of D-FF7.

The outputs of the two AND circuits 6 and 8 are, for example, the OR circuit 9
Is input to the clock input terminal CLK of the up / down counter 10, for example. The output sent from the D-FF7 is added to the up-counting / down-counting counting mode switching terminal U / D of the up-down counter 10.

For example, four output terminals Ao, Bo, Co, Do provided in the up / down counter 10 send a 4-bit range-up signal or range-down signal to the range setting circuit 2. These four output terminals Ao or Do
For example, a 4-input NAND circuit 11 and an OR circuit 12 are connected, and the outputs of the NAND circuit 11 and the OR circuit 12 are
They are applied to the other inputs of the AND circuits 6 and 8, respectively.

To the preset signal input terminals Ai, Bi, Ci, Di provided in the up / down counter 10, for example, a preset circuit 13 having a 4-bit structure is connected, and the preset circuit 13 manually sets a desired signal. It is possible to switch to the range and to set the number of stages of the switching range during auto range.

That is, the preset circuit can be manually operated.
13 to preset terminal PR of up / down counter 10 above
When, for example, a signal of level 1 is applied to, the counting operation of the up / down counter 10 is cleared and the signal from the preset circuit 13 can be input.

Therefore, when a 4-bit signal of (1010) corresponding to a desired range is input from the preset circuit 13, this signal is sent from the output terminals Ao to Do to the range setting circuit 2 through the up / down counter 10. Then, the range is switched to the desired range.

When the automatic range mode is set from this state, the 4-bit signal (1010) manually set as described above is used as an initial value, and the range up or down is performed from the corresponding range. To explain the case of range up, the full count is (111
Since it is 1), it is possible to switch over 6 ranges.

When setting the switching range to 4 ranges, set the initial value to (110
Since it is 4 bits in this example, it is sufficient to set the initial value to (0000) in order to make full use of it and enable 16 range switching.

Next, the operation of the auto range circuit will be described with reference to FIG. In FIG. 1, the same reference numerals are attached to the portions where the signals (a) to (l) or (a) ′ to (l) ′ shown in FIG. 2 appear. Further, the initial value can be arbitrarily set by the preset circuit 13 as described above.

Explaining the case of the range up of FIG. 2 (a), when a relatively high level analog signal to be measured is emitted from the signal source 1 as shown in FIG. Is added to the A / D converter 3 via the, and converted into a digital signal in the A / D converter 3 as shown in FIG. The analog signal to be measured may be current or voltage, for example.

In the A / D converter 3, the level of the measured analog signal is compared with a built-in reference value, and when the level is excessive, as shown in FIG. A range-over signal of level 1 is issued every time, and one input terminal of the AND circuit 6 and D
It is added to the reset terminal R of -FF7.

As a result, the output of D-FF7 becomes level 1 as shown in FIG. 9 (G), and the up / down counter 10 receives this output and the counting mode is up-counted.
In this case, the four bit signals of the up / down counter 10 are rarely all at level 1. For example, if even one of them has a level 0 bit signal, the NAND circuit 11 outputs the same signal as shown in FIG. A signal of level 1 is emitted as shown in FIG. 3 and applied to the other input terminal of the AND circuit 6.

Therefore, on the output side of the AND circuit 6, a level 1 signal (e) similar to the above range over signal (c) appears and is input to the OR circuit 9. As shown in (f), this signal is added from the OR circuit 9 to the up / down counter 10 as a clock signal for up counting.

In the up / down counter 10, the above signal (f)
The output terminals Ao, Bo, Co, D
Each bit signal from o to (h) to (l) is sent to the range setting circuit 2.

That is, in this embodiment, the initial value is set to (1000), and the output terminals Ao, Bo, Co, and Do are (1001) (1
010) (1011) (1100) (1101) (1110) (1111) are output, these signals are converted into binary signals by the decoder in the range setting circuit 2, and, for example, the resistance is switched based on the value. To be However, when the proper range is selected during this switching operation, the range over signal (C) is not sent from the A / D converter 3, so that the range is fixed.

In this way, when the initial value is set to (1000), the range can be switched in 8 steps. When the up / down counter 10 reaches the full count (1111), it is reset by a signal from the range setting circuit 2, for example.

Next, the case of range down will be described with reference to FIG. A range under signal (c) 'is issued from the A / D converter 3 and is applied to one input terminal of the AND circuit 8 and the set terminal S of D-FF7. In this case, all four bit signals of the up / down counter 10 are rarely at level 0. For example, if even one of them has a level 1 bit signal, the output of the OR circuit 12 becomes level 1. .

When this level 1 signal is applied to the other input terminal of the AND circuit 8, the same signal (e) 'as the range under signal (c)' appears on the output side and is input to the OR circuit 9. At the output side of the OR circuit 9, the same signal (F) 'as the signal (E)' appears, and is added to the up / down counter 10 as a clock signal for down counting.

In this case, since the range under signal (c) 'is applied to the terminal S of D-FF7 as described above, its output becomes a signal of level 0 as shown in (g)',
The counting mode of the up-down counter 10 is down-counted.

As a result, the output terminals Ao, Bo, Co, Do output range switching signals for each count toward the full count (0000). In this example, since the initial value is (1000), (0111) (0110) (0101) (0100) (0011) (00
10) A 4-bit range switching signal of (0001) (0000) is sent to the range setting circuit 2.

The range setting circuit 2 decodes this signal and switches, for example, a resistor. In this way, when the appropriate range is selected, the range under signal (c) 'disappears, and the range is fixed to that range.

[Effect of the Invention] As described above, the autoranging circuit of the present invention is
The up / down counter 10, the preset circuit 13 for setting the initial value thereof, the flip-flop circuit 7, and the four gate circuits 6, 8, 11, 12 have a simple structure and are inexpensive.

Moreover, the preset circuit without changing the circuit configuration
The desired range can be set with 13, and the number of range switching steps in the auto range mode can be set arbitrarily, so that the number of ranges varies depending on the function (measurement item) like a digital multimeter. It is also suitable for the measuring instrument.

Furthermore, if this preset circuit 13 is connected to an external control bus or the like, remote range switching from the outside becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment in which the auto-ranging circuit according to the present invention is applied to a digital measuring instrument,
FIGS. 2A and 2B are timing charts of respective signals in the case of range up and range down. In the figure, 1 is a signal source, 2 is a range setting circuit, 3 is an A / D converter, 5 is an auto-ranging circuit, 6 and 8 are AND circuits, 7
Is a flip-flop circuit, 9 and 12 are OR circuits, 10 is an up / down counter, and 11 is a NAND circuit.

Claims (1)

[Scope of utility model registration request] 1. A / D from a signal source through a range setting circuit 2.
The level of the signal under measurement applied to the converter 3 and the above A /
The permissible upper limit level or permissible lower limit level of the measured signal that can be digitally converted by the D converter 3 is compared, and when the level of the input measured signal exceeds the upper limit level or does not reach the lower limit level. When above
In response to the first and second gate circuits 6 and 8 for selectively passing the intermittent signals respectively emitted from the A / D converter 3 as the clock signal for counting, and the intermittent signals emitted when the upper limit level is exceeded. A flip-flop circuit 7 that outputs an up-counting mode signal and outputs a down-counting mode signal in response to an intermittent signal generated when it does not reach the lower-limit level, and the upper-limit level by the up-counting mode signal from the flip-flop circuit 7. The intermittent signal generated when the value exceeds the limit is up-counted, and the intermittent signal generated when the lower limit level is not reached is down-counted by the down-counting mode signal from the flip-flop circuit 7 to switch the range up or range down. Up-down counter 10 for sending the data to the range setting circuit 2
A preset circuit 13 capable of arbitrarily setting the range of the range setting circuit 2 by giving a signal corresponding to a desired range to the up / down counter 10, and the first and second gate circuits 6 and 8. A NAND gate circuit 11 which is interposed between the output side of the up-down counter 10 and the output side of the up-down counter 10 for turning on / off the first gate passage of the intermittent signal and a second gate passage of the intermittent signal. An autoranging circuit having an OR gate circuit 12 for controlling ON and OFF of the.