# SGX-4H2S-100 Industrial Hydrogen Sulphide (H2S) Sensor

#### Tiong

Joined Dec 5, 2019
4
Greetings everyone! I am currently designing a sensor array that will be used to detect the gases released by the durian. One of the sensors used is the SGX-4H2S-100 Industrial Hydrogen Sulfide (H2S) Sensor. From the datasheet, it says that the output signal is 1200+-250 nA/ppm. Thus, may I ask, with the circuit design shown below, am I reading the output value coming out of the sensor correctly?

The calculation of the 33k ohm is done as shown below:
From the datasheet, the output signal is 1200+-250 nA/ppm. So the maximum value of 1450 nA/ppm was used in the calculation. Other than that, the datasheet also shows that the measuring range is 0–100 ppm. Thus, the maximum concentration of gases that the sensor will be able to detect is 100 ppm. Then, the maximum output signal will be 145nA ( 100ppm*1450nA/ppm). Since the VDD of the ADS1115 is 5V, then the maximum ADC voltage able to be read by the ADS is 5V. Using Ohm's Law, V=IR , the calculated resistor value will be 34482.76 ohms. Thus, a 33K ohm resistor was chosen.

So my question is :
(i) Am I designing the circuit correctly?
(ii) Is there anything I need to take note of on the SGX-4H2S-100 datasheet?

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#### Ian0

Joined Aug 7, 2020
9,434
100ppm*1450nA/ppm is 145μA, but from there you managed to get 33k correctly.
The data sheets specifies a maximum open circuit voltage of 1.3V, but it is in the intrinsic safety section , and it also recommends a load resistor of 10Ω, both of which are rather confusing.
My suggestion would be to ask the manufacturer of the sensor for any application data, or suggested application circuits.