JPH03293545A - Dew condensation detector - Google Patents

Abstract

PURPOSE:To prevent a trouble of sticking of a tape or the like with an accurate detection of a dew condensation state by preserving a dew condensation detecting state by a preserving means even when a power source is cut even while this state is going on to make a dew detection state ready forcibly for a fixed time when the power source is closed again. CONSTITUTION:When a power source is turned OFF, an electric charge of a capacitor C2 flows to the base side of a transistor Tr3 so that a dew condensation detecting state is preserved and stored while the electric charge stored in the capacitor C2 is discharged. Then, when the power source is closed again to turn ON a transistor Tr2, an output V3 of a comparator 10 is ground forcibly to go to L to output a dew condensation detection to a Vout.. Then, a dew condensation detector 1 detects a dew condensation based on a signal from a moisture sensor 2 and sends a signal to a control section 5, which activates 51 a heater to perform a heating with the heater 52. A motor is driven to operate the motor 56 and a guide roller 57 is moved to separate a tape from a cylinder 39.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a dew condensation detection device.

<Prior Art> A dew condensation detection device is used in a video tape recorder, a DAT, etc. to detect dew condensation inside the device. This dew condensation detection device is configured to detect a dew condensation state by comparing the output of a normal humidity detection sensor with a predetermined reference signal using a comparator. In addition, a hysteresis characteristic is given to the operation of the comparator, and this is used to set the humidity at which the dew condensation state is released to be lower than the humidity at which the dew condensation state is initially detected, thereby making the prevention of dew condensation more complete.

FIG. 4 shows a circuit diagram of this conventional dew condensation detection device.

In the conventional device, a comparator 10 connects an input voltage v2 that varies depending on the resistance value of the humidity sensor 2 and a reference voltage v1.
The configuration is such that it is detected whether the humidity is equal to or higher than the initial detection humidity a of dew condensation shown in FIG. Mo and Vl<
When the voltage is V2, that is, when the humidity is high and there is condensation, v
3 becomes "L". As a result, transistor Tri is turned off.

The configuration is such that the output VOUT becomes "H" indicating a dew condensation state. Devices such as video tape recorders are usually configured so that this H output drives a heater to eliminate dew condensation within the device.

When the output v3 becomes L, vl changes to a lower value than when detecting dew condensation because feedback is applied by the resistor R7. That is, the comparator 10 has hysteresis, and as a result, unless the dew condensation release humidity is lower than the initial dew condensation detection humidity a shown in FIG. 3, V3 will not become "H" and the dew condensation detection state will not be released. It has become. This is called the normal dew condensation detection extended state, and the set values of this state, ie, the initial dew condensation detection humidity a and the dew condensation release humidity s, can be changed as appropriate by appropriately selecting the values of the resistors R1 to R8.

<Problems to be Solved by the Invention> However, the conventional dew condensation detection device detects dew condensation in an extended dew condensation detection state, that is, in the initial detection humidity a of dew condensation.

If the power is cut off even momentarily when the humidity has become lower than the initial detection humidity a of condensation and higher than the dew condensation release humidity a after heating with a heater etc., the comparator will not function even if the power is turned on again. Since the reference voltage v1 of No. 10 returns to the voltage corresponding to the humidity a detected at the initial stage of condensation, the detection device has a drawback that it does not enter the dew condensation detection state. Therefore, there is a problem that the dew condensation detection state is not reached until the dew condensation is not sufficiently removed, and there is a risk of accidents such as tape sticking.

Means for Solving the Problems> The present invention has been made to solve the problems of the conventional dew condensation detection device described above. A hysteresis comparator that stores the condensation detection state just before the power is turned off, and a means to force the condensation detection state for a certain period of time when the power is turned on again only if the condensation detection state was the state immediately before the power was turned off. The basic feature is that it is equipped with means for

Function> If the power is cut off during the dew condensation detection state, this state is saved by the storage means. When the power is turned on again, the condensation detection state is forcibly maintained for a certain period of time. 6. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of this dew condensation detection device incorporated into a video tape recorder.

This dew condensation detection device W1 has a humidity sensor 2 mounted inside the video tape recorder, and is configured to detect the state of dew condensation inside the recorder. As mentioned above, the humidity sensor 2 is an element having the characteristics shown in FIG. 3 and whose electrical resistance changes depending on the ambient humidity.

The dew condensation detection device M1 detects dew condensation based on the signal from the humidity sensor 2, and sends the dew condensation detection signal to the control section 5. The control unit 5 is configured to control the heater drive unit 51 to heat the heater 52 based on this detection signal. Further, by sending a command to the motor drive unit 55 and activating the motor 56, the guide roller 57 is moved and the tape is separated from the cylinder 59. If condensation occurs inside the recorder due to this operation, the condensation is removed by heating and the tape is prevented from sticking.

The details of the dew condensation detection device 1 will be explained based on the circuit diagram of FIG.

The structure of the upper half of FIG. 1 is the same as the conventional circuit shown in FIG. 4, and the same parts are given the same numbers.

In addition to the conventional configuration described above, a return circuit 11 is further provided in the lower half. In this recovery circuit 11, the output v3 of the comparator 10 is connected to GND via an NPN transistor Tr2 and a transistor Tr3 connected in series. The transistor T r 2 is configured to be turned on for a period of time defined by the capacitor C1, the resistor R12, and the resistor R13 when the power is turned on.

On the other hand, the transistor Tr3 is turned on by outputting V o u and is turned on for a predetermined time by discharging the charge accumulated in the capacitor C2. This predetermined time is determined by the values of capacitor C2 and resistor R14. Capacitor c2 is connected to V via diode D2.
It is designed to be charged by connecting it to the output. Further, a bypass transistor Tr4 is connected in parallel to the capacitor c2, and this transistor Tr4
is turned on by the output v3 of the filter 10. Since v3 is H when dew condensation is not detected, the transistor Tr4 is turned on and the capacitor C2 connected in parallel with the transistor Tr4 is not charged. However, when dew condensation is being detected, since v3 is L, the transistor Tr4 is turned off and the capacitor C2 is charged. When the power is turned off in this state, the transistor Tr4 is off and the current is cut off by the diode D2, so all the charges in the capacitor C2 flow to the base side of the transistor Tr3 and are accumulated in the capacitor C2. The dew condensation detection state is stored while the accumulated charge is discharged, and the transistor Tr3 is configured to maintain the on state during this time. When the power is turned on again in this on state and the transistor Tr2 is turned on, the output v3 of the comparator 10 is forcibly grounded and becomes L, so that V out outputs the lateral ratio of dew condensation. There is.

Next, the operation will be explained.

In a non-condensing state, Vl>V2, so v3
becomes “H”, transistor Tri is turned on, and
VOUT becomes "L". At this time, transistor Tr4
is on, and the capacitor C2 is not charged. On the other hand, when the humidity sensor 2 detects dew condensation, Vl<V2, so ■3 becomes "L", and as a result, the transistor Tri turns off and V OUT becomes "L".
H'' and dew condensation is detected.At this time, the transistor Tr
4 is off. Therefore, capacitor C2 is charged through diode D2. At the same time, the transistor Tr3 is turned on.

When the power is cut off in this state, the charge stored in the capacitor C2 flows through the resistor R14 as a base current of the transistor Tr3.

As a result, the transistor Tr3 remains on as long as the current remains at a predetermined level or higher even after the power is cut off. That is,
Even if the power is cut off when the condensation is not detected, the transistor Tr3 remains off, but when the power is cut off while the condensation is detected, the transistor Tr3 is turned on for a predetermined period of time after the power is cut off. That is, the dew condensation detection state is stored and stored by the capacitor C2.

Subsequently, when the power is turned on again, at the same time, the transistor Tr2 is turned on for a predetermined time determined by the capacitor C1, the resistor R12, and the resistor R13. the result,
When the power is turned on again when the transistor Tr3 is turned on in the dew condensation detection state when the power is cut off, both the transistor Tr4 and the transistor Tr2 are turned on. As a result, v3 is forcibly set to "L", and a condensation state detection state is entered. At this time, if the humidity is still in the dew condensation state and the humidity is above b and V2>Vl, the L state of v3 continues. At this time, if the equipment has dried and the humidity is below b and V2<Vl, when transistor Tr2 is turned off,
That is, after a time period determined by the capacitor C1 and the resistors R12 and R13 has elapsed, v3 becomes H and dew condensation detection ends. Note that when the power is turned on, if the charge in the capacitor C2 is not enough to turn on the transistor Tr3, v3 becomes L.
do not become.

While the Vout is on, the control unit 5 correspondingly sends a command to the heater operating unit 51 to heat the heater 52. Further, a command is sent to the motor rotating section 55 to operate the motor 56, thereby moving the guide roller 57 and separating the tape from the cylinder 59.

As the equipment continues to dry, the output of humidity sensor 2 decreases and V2
<Vl, v3 is H, Trl is on, and V o
ut becomes L. The control unit 5 detects this and returns from the dew condensation response operation to the normal operation. At this time, the condensation on the equipment has cleared. Also, at this time, the transistor Tr4 is turned on, and the charge in the capacitor C2 is discharged via the resistor R15. Therefore, even if the power is turned off and then turned on again in this state, v3 will not become L.

Note that, from the viewpoint of accident prevention, it is preferable that the storage time of the dew condensation detection state determined by the values of the capacitor C2 and the resistor R14 be several minutes, which is about the same as the dew condensation detection extension time, but a shorter time is also effective.

In the embodiment described above, during the dew condensation detection extended state.

In other words, if the humidity after dew condensation is detected is below the condensation state detection humidity a and higher than the dew condensation release humidity, the condensation detection state will be saved even if the power is cut off due to a power outage, etc., and when the power is turned on again, the humidity will be forced for a predetermined period of time. The dew condensation detection can be extended automatically. Therefore, even after the power is turned on again, the dew condensation prevention operation can be continued for a predetermined period of time, and accidents such as tape sticking to the head can be prevented.

<Effects of the Invention> As explained above, the dew condensation detection device of the present invention includes a sensor that detects humidity, a hysteresis comparator that compares the output of the sensor with a reference value and hysteresis, and a device that detects condensation immediately before the power is turned off. It is equipped with a means to save the state and a means to forcibly enter the condensation detection state for a certain period of time when the power is turned on again only if the state immediately before the power was turned off was in the condensation detection state. Even if the power is cut off, this state is preserved by the storage means, and when the power is turned on again, the dew condensation inspection state is forced for a certain period of time. Therefore, when the power is turned on again, it is possible to more reliably detect the condensation state and perform dew condensation prevention operations, thereby achieving effects such as being able to prevent accidents such as tape sticking. Can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram 1 and 2 showing an embodiment of the present invention.
The figure is a block diagram showing the configuration of a dew condensation detection device installed in a video tape recorder, FIG. 3 is a characteristic diagram of a humidity inspection sensor, and FIG. 4 is a circuit diagram of a conventional dew condensation detection device. 1: Condensation detection device, 2: Humidity sensor, 5: Control unit, 10
: Comparator, 11: Return circuit, 51: Heater active part, 52: Heater, 55: Motor drive part, 56: Motor,
57; Guide roller, 59 Nijilinda, a: Initial detection humidity of condensation, b: Condensation release humidity. Patent applicant Clarion Co., Ltd.

Claims (1)

[Scope of Claims] A sensor for detecting humidity, a hysteresis comparator for comparing the output of the sensor with a reference value and hysteresis, means for storing a dew condensation detection state immediately before the power is turned off, and the power is turned off. A dew condensation detection device comprising: means for forcing the condensation detection state for a certain period of time when the power is turned on again only if the previous state was the condensation detection state.