Measuring NH3 and CO gas

[amindzo]

Hi, i want to measure the ammoniac and CO gas in aviculture and when they go high(higher than the favorite value) pic microcontroller turn the alarm on.
note: i wan to measure the value,not just specify the leakage.
which sensor i should use? (digital one is better)

 

[jpanhalt]

Based on the chemistry of ammonia and CO, I think you will need two sensors; although, they might have a common readout module. Some mass spectrometric based, handheld sensors can measure both*, but I assume that is not what you are considering.

Are there any specific sensors you are considering and want comments regarding?

John

*Edit: Remember CO and N2 have the same nominal mass, so you need a fairly high-resoluton MS to tell them apart.

 

[Speakerguy]

Ammonia is NH3, so that might help CO detectors are pretty easy to come by.

 

[amindzo]

could you introduce me some sensors?

 

[Hero999]

CO is flammable so a hot wire sensor would work but it might not be sensitive enough for your application though.

I don't know about ammonia though. The only thing I can think of at the moment is a piece of moist paper with a pH sensor.

 

[amindzo]

Hi, i found MQ137 for ammoniac gas and MQ7 for CO gas, you can see the datasheet in this site:
**broken link removed**

**broken link removed**

could you help me to connect these sensors to PIC16F877A? could you help me with the code? i haven't word with these sensors, i've worked with digital sensors.
i use picbasic pro 2.43

thank you

 

[jpanhalt]

On my computer, the MQ137 is shaded and does not come up as an active link. It may not be available yet.

The MQ7 is active. It seems to have a very slow response time and is probably more suitable for static measurements, for example at a fixed location in a mine.

If you check the methane monitor, a typical analog circuit is given. The driver and output functions might give you some ideas of how to do much of the same with a PIC. Although, when you consider the current needs of the sensor, you might be better off (i.e., simpler)just building a similar analog circuit and using the PIC only to monitor output.

John

 

[amindzo]

I saw that but it has some things that not clear

 

[amindzo]

Hi, first look at basic test circuit of MQ137 that i attached you (JPG file). We have this formula in the datasheet:
Rs=((Vc/VRL)-1) × RL

Rs= Resistance of the sensor
Vc= +5 volt
VH= +5 volt
my application is alarming when NH3 concentration reaches or wants to go higher than 25ppm.
So i can measure the VRL value(voltage) and put this value in the formula to find the Rs value.
1- What value of RL are you suggest for my application?
2-What's the value of the Rs in 25ppm NH3?
3- The Rs value and the gas concentration in ppm have the inverse ratio or direct ratio? ( i think it's inverse ratio)

If i have RL value and measuring the VRL, i will put these values in the formula and find the Rs value.
If i have Rs value in 25ppm NH3(standars vaule of Rs for MQ137 in 25ppm that you will tell me), i compare the Rs value from the formula ( result of the formula) with the Rs value in 25ppm NH3 (the standard value that you will tell) and when they are equal or when the measured value lower than the standard value(that you will tell) i will turn on the alarm because when thay are equal or the measured value is lower than the standard value( that you will tell me) the gas concentartion is 25ppm or more than 25 ppm.(beacuse i think they have inverse ratio, if they have direct ratio, when the two value Rs reaches to each other or the measured value wants to go haigher than the standard value i will turn on the aralm)
I think it's the best way to alarm when gas concentration reaches or wants to go higher than 25 ppm.
please answer those three questions.

Thank you very much

 

[amindzo]

i want to make an intelligent monitoring system for aviculture that measure temperature,humidity and ammonia concentration and depends on the situations it turning on the fans,heater and etc. this system should alarm when ammonia concentration reaches or wants to go higher than 25ppm. i wanted to use MQ137 but it's difficult for me to calibrate the sensor because i don't have a chamber test or experimental environment so i think i should use ME3-NH3 because there is a linear relashionship between NH3 concentartion and output current and i don't need to calibrate it in a chamber test or experimental envirnoment.Am i thinking right?
the datasheet is not complete,it has no explain about the pins.
i have this application circuit(attached file),could you explain more about the circuit and how does it work? what's the output of this circuit(SING1)? i want to connect this sensor to PIC microcontrollers.could you explain about response time?

 

[amindzo]

Any answer?