JPH0548125Y2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) This invention is a carbon monoxide gas sensor (CO sensor)
The present invention relates to a temperature compensation circuit.

(Conventional technology and problems) Conventionally, a thermistor has been used to compensate for the off-level temperature of the CO sensor. In this case, as shown in Figure 2A, the temperature characteristics of the thermistor are such that the resistance value decreases as the temperature increases (Rd→
On the other hand, as shown in Figure 2B, the temperature characteristic of the CO sensor is that as the temperature rises, the resistance value decreases until a certain temperature (RD→
RB), the resistance value reaches its minimum at a certain temperature, and conversely increases in the higher temperature range (RB→
RA). Normally, the detection level of the CO sensor is set stepwise using multiple comparators with different reference voltages, but in this way, the resistance value of the CO sensor is lower than the upper limit of the operating temperature range. If it is the minimum,
The output level of the comparator whose output is turned on in a temperature range higher than the temperature range where the detection level is minimum becomes low, making it impossible to perform appropriate temperature compensation, that is, setting the detection level.

In view of these circumstances, the present invention aims to provide a detection level setting circuit for a carbon monoxide gas sensor, which can smoothly set the detection level of a CO sensor in response to temperature changes. Hereinafter, the present invention will be explained in detail based on illustrated examples.

(Example) In Fig. 1, 1 to 4 are each comparator, 5
is a thermistor, 6 is a CO sensor, R1 to R10 are each resistance, and V1 to V5 are voltages at each point.
Here, V2>V3>V4, and comparators 1 and 2 input reference voltages V2 and V3 to their negative phase input terminals, respectively, and input the thermistor output V1 to their positive phase input terminals, whereas only comparator 3 Input the reference voltage V4 to the positive phase input terminal, and the thermistor output V
1 is input to the negative phase input terminal. Therefore, the thermistor output V1 and each reference voltage V
The positive phase input level V5 of the comparator 4, which sets the detection levels VA to VD of the CO sensor 6, is as follows depending on the magnitude relationship with V2 to V4.

When V1<V4 V5=VA={(R7R8)Vcc}/(R6+
R7R8) V1=V1a=(Ra・Vcc)/(R1+Ra) When V4<V1<V3 V5=VB={(R7R8R9)・Vcc}/
(R6+R7R8R9), V1=V1b=(Rb・Vcc/(R1+Rb) When V3<V1<V2 V5=VC={(R7R9)・Vcc}/(R6+
R7R9), V1=V1c=(Rc・Vcc)/(R1+Rc) When V1>V2, V5=VD=(V9・Vcc)/(R6+R9), V1=VD=(Rd・Vcc)/(R1+Rd), here So, if R9>R8, then R7R8R9<R7R8<R7R9<
R9 Therefore, thermistor resistance value Ra<Rb<Rc<Rd
On the other hand, the potential relationship is VB<VA<VC<VD.

(Effects of the invention) As described above, the present invention allows the reference voltage input terminal of the comparator and the input terminal of the thermistor output, which sets the detection level corresponding to the temperature range where the temperature characteristics of the CO sensor is reversed, to correspond to other temperature ranges. Since it is in the opposite phase to the comparator that sets the detection level, the detection level can be set according to the temperature characteristics of the CO sensor, and appropriate temperature compensation can be performed.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2A
is the temperature characteristic diagram of the thermistor, and FIG. 2B is the temperature characteristic diagram of the CO sensor. 1 to 3...Comparator, 5...Thermistor,
6...CO sensor.

Claims (1)

[Scope of utility model registration request] A thermistor is used to compensate for the temperature of a CO sensor, which has a temperature characteristic in which the resistance value decreases as the temperature rises up to a certain temperature, and above that temperature, the temperature characteristic reverses and the resistance value increases. Input the output of a circuit containing a thermistor whose output changes with temperature changes to the input terminal,
The other input terminal includes a plurality of comparators that input predetermined reference voltages, a reference voltage adjustment circuit whose reference voltage output changes depending on whether the outputs of the plurality of comparators are turned on or off, and a CO sensor. A CO sensor circuit whose output changes depending on the CO detection level, and a comparator which inputs the output of the reference voltage adjustment circuit to one input terminal and inputs the output of the CO sensor circuit to the other input terminal. , wherein at least one of the plurality of comparators corresponding to a temperature range in which the output of the CO sensor circuit is inverted due to temperature characteristics has an input having an opposite phase with respect to the other comparators. Temperature compensation circuit for CO sensor.