AN4348 datasheet(21/25 Pages) STMICROELECTRONICS

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AN4348

Testing the hardware

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Testing the hardware

Different tests can be performed to check that the hardware is functional.

Test 1

Remove the sensor (normally sensors are not soldered or they would be damaged)

Short the RE and the CE on the PCB.

On this node, check that the reference voltage is obtained (note that the op-amp is

now configured in buffer configuration)

Still working without the sensor, verify the output of the second op-amp. It should be at

the WE voltage as this op-amp is also in buffer configuration since Rload is left open.

Both the RE and the WE voltages can be fine-tuned in this way.

Test 2

Add a current source on Rload to check that the trans-impedance amplifier is operating

correctly (Vout should equal VWE+RT×I)

Try the application with the sensor (first removing the short circuit and the current

source).

In the absence of the targeted gas, Vout = VWE. During exposure to the gas, the output

should vary according to the sensitivity of the sensor. Note that if the sensor was left

unbiased, it may take several minutes up to several hours for it to operate correctly.

As the sensitivity of the sensors is not well controlled during their manufacturing, it is

necessary to calibrate your application with different gas concentrations.

Alternatively, a quick reading can be taken by performing a bump test. This is the sudden

exposure to a gas, for example, in the case of O2 sensing, it is the measurement of an

exhalation.

Figure 12 illustrates the result obtained with a three-electrode CO sensor using the

TSU101.

Figure 12: Response to a carbon monoxide step using the TSU101

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