conversion of gas concentration into 4-20 mA output!!!!!

[paddy_p]

Hi,

Please have a look on a below mentioned link.

**broken link removed**

I need a gas detector circuit which detects concentration of gas and gives 4-20 mA output as per gas concentration.

I am bit confused in a circuit provided in that link.

Can you please explain me how this circuit works?

Thanks,
paddy

 

[crutschow]

The circuit is powered by the combination input power/output current signal. You apply +7.5V to +35V DC to power the circuit. The circuit uses several op amp circuits to amplify the signal from the sensors and adjust the base of transistor TR2 to control the power input current to be between 4-20mA as determined by the sensor signals and pot settings. You measure this input current to extract the signal information.

Is that clear?

 

[paddy_p]

Thanks crutschow.

I have got a little idea about this circuit. I will check out it's results.

Thanks,
paddy

 

[paddy_p]

Hiii,

I have to design circuit for gas detector for toxic as well as explosive gases.

**broken link removed**

I am using the sensor mentioned in above link for explosive gases.

Can I use instrumentation amplifier to amplify the senor output signal?

I have to provide potentiometers for Zero and span setting.

Please advice how to do it.

thanks,
paddy

 

[crutschow]

You could use an instrumentation amp but they are normally used for differential signals and your signal is single-ended, so a standard op amp circuit would work. You might also try this IC or this as a starting point.