Changing threshold for 1162HV cards?

[josep_ca]

I am working on an application and I was using a 1162HV card on a SCXI chassis to detect voltages up to 32 V. The only problem that I have is that the application is suppose to detected voltage inactivity if the input voltage is less than 3 V. The threshold of the card is a bit low for that. According to the manual is 2 V in the laboratory even voltages greater than 0.8 volts are enough to trigger the activity line on the 1162HV card.
I wonder if it’s possible to modify the voltage threshold of the card by modifying some of the resistor inside the card or any circuitry to increase the threshold or if there is a particular configuration I can use to obtain the same goal.

[LYu]

Hi Josep_ca,

It may be possible to use a resistor at the input channel to act as a voltage divider and raise the threshold value. I'm trying to verify if any other issues might be affected by this solution. I'll get back to you soon.

Thanks,
Lesley Y.
Applications Engineering

[LYu]

Hi Josep_ca,

The input threshold can be raised by putting a resistor inline with your signal. The extra resistor together with the impedance of the input circuitry will act as a voltage divider. The result is that the 1162HV module sees a smaller voltage potential between INa and COM.
V/(Ro+R') = V'/Ro
V/V' = (Ro+R')/Ro
In this case, V/V' = 3

So with the right resistor a 3V signal between INa' and COM will appear as a 1 V signal. See the figure below. Selecting the right resistor is best done by selecting a resistance and then adjusting it up and down as needed.

Hope this helps.

Thanks,
Lesley Y.

[josep_ca]

Thanks Lesley, it makes sense your solution. I will try it.