JPH0525036Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Industrial application field] This invention focuses on the fact that the catalytic combustion gas sensor has almost linear characteristics both initially and over time, and the output of the same element in clean air. This invention relates to a portable gas alarm with a zero check function that allows alarm settings to be indirectly calibrated by adjusting the alarm to zero.

[Conventional technology]

Conventionally, in a gas alarm device that issues an alarm when the concentration exceeds a predetermined concentration, in order to check the alarm concentration, gas having a predetermined concentration is actually produced and this gas is supplied to the gas alarm device for inspection. By the way, there are two causes for fluctuations in alarm concentration: fluctuations in the sensitivity of the gas sensor of the gas alarm to gas, and fluctuations in the output value in clean air, that is, the zero point. In this case, the latter is larger.

[The problem that the idea aims to solve]

When using a catalytic combustion type gas sensor, alarm concentration fluctuations can be suppressed to a considerable extent by adjusting the zero point every time a measurement is made, but with conventional gas alarms, there is no zero check to see if the zero point has been adjusted. The disadvantage was that it could not be done easily.

This invention was made to eliminate the above-mentioned drawbacks, and the object is to provide a portable gas alarm that can automatically perform a zero check.

[Means to solve the problem]

The portable gas alarm with zero check function according to this invention includes a bridge circuit configured of a catalytic combustion type gas sensor, a compensation element, and a variable resistor for zero check, which are connected in series to a power source.
It is equipped with a comparator that takes as input the reference voltage generated by dividing the output of the variable resistor using multiple resistors and the output of the gas sensor of the bridge circuit, and outputs an alarm output when the output of the gas sensor exceeds the reference voltage. In a gas alarm, the first contact inputs the output of the variable resistor to the comparator as the first signal without going through multiple resistors when closed, and A second contact point that generates a second signal whose level is lowered is provided.

[Effect]

In this device, when one of the two contacts is closed, the output of the variable resistor is input to the comparator as the first signal without going through multiple resistors, and when the other contact is closed, the output of the variable resistor is input as the first signal. By generating a second signal at a level slightly lower than the level of the gas alarm and inputting it to the comparator, the variable resistor for zero check is adjusted so that the gas alarm sounds with the first signal and does not sound with the second signal. A zero check is automatically performed and alarm settings are calibrated indirectly.

〔Example〕

. FIG. 1 is a block diagram showing the overall configuration of an embodiment of this invention, and FIG. 2 is a circuit diagram showing details of the zero check circuit in FIG. 1.

In FIG. 1, 10 is a gas sensor, 20 is a zero check circuit, 30 is a comparator, 40 is an alarm display drive circuit, 50 is a buzzer, 60 is an LED,
70 is a constant voltage circuit, 80 is a battery, and 90 is a power supply circuit, which converts the voltage of the battery 80 into a voltage suitable for each part and supplies it.

To outline this operation, zero point adjustment is performed by the zero check circuit 20, as will be described later.
After that, when the gas sensor 10 detects gas, its output enters the comparator 30 and is compared with a reference potential, and if the output of the gas sensor 10 is below the reference potential, that is, if the gas concentration is above a predetermined value, an alarm is displayed. The drive circuit 40 operates and the buzzer 5
0 sounds and the LED 60 lights up or blinks to issue an alarm.

Next, the zero check performed by the zero check circuit 20 will be explained with reference to FIG.

In Fig. 2, e is a catalytic combustion type gas sensor, e' is a compensation element serving as a load resistance, and VR is a variable resistor, and these constitute a bridge circuit.
A DC voltage of the power supply is applied between points A and B, and the output of the bridge circuit appears between point C indicating the output of gas sensor C and point D indicating the output of variable resistor VR.
R ₁ to _{R 3} are resistors, S ₁ is the first contact, and S ₂ is the second contact. When the first contact S ₁ is turned on, points D and E are short-circuited, and the second contact is turned on. When contact _S2 is turned on, points D and F are shorted. In the operating state after the zero check, the potentials at points C and E are input to the comparator 30. Since the gas sensor e needs to be kept at a constant high temperature, it is necessary to keep a constant current flowing through it. For this purpose, load resistance,
Since the reference voltage is determined by the type of gas, it is connected in series with the compensation element e', which is a load resistance, to the power supply.

In FIG. 2, the variable resistor VR is initially set during manufacturing so that the potential V _C at point C and the potential V _D at point D in the atmosphere are equal. Next, the potential corresponding to the gas concentration you are trying to set
The value of resistor R ₁ is chosen so that V _C and V _E are equal.

Next, the operation will be explained. When gas is detected, the resistance value at both ends of gas sensor e increases, so the potential at point C decreases, and when the potentials at point C and point E become the same, an alarm output is output from the comparator 30, as described above. A warning will be issued.

Before performing this operation, a zero check is performed, but
The method is as follows.

First, the first contact S ₁ is closed in clean air.
As a result, the potential of 'E becomes the same as the potential of 'D, and in this state, the variable resistor VR is adjusted to issue an alarm. Next, when the first contact S ₁ is turned off and the second contact S ₂ is closed, point F, which is slightly higher than point E, has the same potential as point D. i.e. resistor
Since both ends of _R1 are shorted, the potential at point D is the resistor.
Since the voltage is divided between R ₂ and R ₃ and the potential at point E is lower than when the first contact S ₁ was closed, no alarm is generated.

In this way, by adjusting the variable resistor VR so that an alarm is issued when the first contact S ₁ is closed, and not when the second contact S ₂ is closed, zero adjustment can be performed automatically. , a zero check will also be performed, indirectly calibrating the alarm settings. and,
The degree of accuracy with which zero adjustment is achieved depends on the degree to which the intended change in alarm concentration is adjusted by this operation. Generally, the gas concentration of a catalytic combustion type gas sensor e and the output of the bridge circuit are linear, so for example, the initial setting concentration is 0 to 5.
If you want to return it to %, just set it to R ₂ /R ₂ +R ₃ = 0.05.

Note that the adjustment error that occurs during the above adjustment is due to the resistor.
This is due to the voltage generated at _R2 , but this value may be determined to a value that does not cause any practical problems.

Furthermore, it goes without saying that the first contact S ₁ and the second contact S ₂ can be of various types.

[Effect of idea]

As explained in detail above, this invention is based on the first method that inputs the output of the variable resistor to the comparator as the first signal without passing through the plurality of resistors when the variable resistor is closed.
, and a second contact that generates a second signal whose level is lower than the first signal level by a certain level in advance when the variable resistor is adjusted. A second warning was issued when the door was closed.
If an alarm does not occur when the contact is closed, it can be immediately confirmed that the zero adjustment has been completed. Therefore, zero adjustment and zero check can be performed on-site in clean air without using other calibration equipment. It has some excellent practical effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of this invention, and FIG. 2 is a circuit diagram showing details of the zero check circuit in FIG. 1. In the figure, 10 is a gas sensor, 20 is a zero check circuit, 30 is a comparator, 40 is an alarm display drive circuit, 50 is a buzzer, 60 is an LED, 70 is a constant voltage circuit, 80 is a battery, 90 is a power supply circuit, and e is catalytic combustion. gas sensor with the formula, e' is a compensation element, VR is a variable resistor, R ₁ to _{R 3} are resistors, S ₁ is the first contact, S ₂
is the second contact point.

Claims (1)

[Scope of utility model registration request] A bridge circuit consisting of a catalytic combustion type gas sensor, a compensation element, and a zero-check variable resistor connected in series to a power supply, and a reference generated by dividing the output of the variable resistor using a plurality of resistors. In the gas alarm device, the comparator is provided with a comparator that receives a voltage and the output of the gas sensor of the bridge circuit and outputs an alarm output when the output of the gas sensor exceeds the reference voltage. a first contact that inputs an output to the comparator as a first signal without passing through the plurality of resistors; and a second signal that generates a second signal whose level is lower than the first signal level by a predetermined level when closed. A portable gas alarm with a zero check function.