MR 513 Alcohol Sensor

[Tanyon]

Hi guys !

I'm working on the Mr513 gas sensor, you can find the datasheet here, and a good drawing from Reloadron here. However I don't understand why when I tried to measure the resistance of C and D I have nothing on the ohmmeter ! Has someone managed to get some good results? Also in a wheastone bridge we suppose that there is 3 resistances whom we know their values but in the previous drawing we only know 2 out of 4.

Thank you to share your experiences.

Tanyon.

 

[Misterbenn]

When you say 'nothing on the ohmmeter' do you mean zero ohms or high/out of range ohms?This is a semiconductor sensor so it will have a polarity and will likely show OC if reversed biased. Other things I'd check - did you have the meter on the right setting, were you powering the circuit at the time?

Anyway why are you trying to measure its resistance? Just connect it up to 3V and measure the output. Remember the output is only as stable as your input!

 

[Reloadron]

OK, good move with the new thread. You should be able to measure across C and D (C to C and D to D) and see something around 2K Ohms. I believe C&D are independent of each other. You add the resistors to make the bridge.

You would add R1, R2 and the potentiometer.

Also by Nothing I assume open circuit or infinity?

Ron

 

[Misterbenn]

I might be wrong but from my reading of the datasheet the bridge is incorporated into the device. So you shouldn't need any other discrete components just input and output.

you can easily check with a quick measure of resistance between the pins

 

[Reloadron]

I might be wrong but from my reading of the datasheet the bridge is incorporated into the device. So you shouldn't need any other discrete components just input and output.

you can easily check with a quick measure of resistance between the pins

Beats the heck out of me. I don't see the pot being part of it though? I have no clue if it is a complete bridge circuit or not.

Ron

 

[Tanyon]

Thank both of you.

When you say 'nothing on the ohmmeter' do you mean zero ohms or high/out of range ohms?T

I mean nothing even a very small value !

Other things I'd check - did you have the meter on the right setting, were you powering the circuit at the time?

Yes I think i did the right setting for the meter. And I tried both: when powering and not.

Anyway why are you trying to measure its resistance? Just connect it up to 3V and measure the output.

I try to measure the resistance of C and D because "the white coil resistor change detecting gas concentration" according to the datasheet, so it remains that C and D are some variable resistances any way! So i would like to see their values modified when we put some alcohol near to the MR513 before trying to see the value of the output.

I confirm that the bridge is not incorporated in the sensor.

We are waiting to receive 2 new sensors because we fear we broke the only sensor we had by powering it at 5V........ So i will give you some new feedbacks when we try the new sensor.


In a wheaststone bridge:

we suppose we know R1, R2 and R3 is variable but here, in our schematic I don't see the wheaststone bridge really.

Charles.

 

[Reloadron]

In your bridge example make R1 = 2K, R2 = 2K R3 = 2K and Rx = 2K. Apply any voltage you would like. What would Vg be? In your bridge Rx is an unknown resistor. If we make R2 a variable resistor and when we begin to vary (adjust) R2 when R2 = Rx the bridge will be balanced. Vg is a galvanometer and will = Zero.

I confirm that the bridge is not incorporated in the sensor.

I sort of thought that was the case. Now in the drawing in post #3 there are two elements, they are D (Detector) and C (Compensation). Without any gas applied they will have the same resistance. Without any gas applied any temperature change on D will have the same change on C. Therefore, without any gas applied the bridge will be balanced. When gas is applied only D (the detector) will change resistance and cause an imbalance in the bridge. That imbalance will show up as Vg.

Take two 3 Volt common flashlight bulbs or lamps. Gently break the glass envelopes to expose the filaments. Use them in your bridge where one is D and one is C. When the D filament is exposed to alcohol (or any explosive vapor) the bridge will be imbalanced.

You likely toasted your sensor(s). Let's see what happens when you get new sensors.

Ron