I have an ADC 22 and two ADC 16 units. The measurements obtained via these units, in particular the ADC 22 seemed suspect.
To prove this I shorted all ADC 22 inputs to the two ground pins on the connector via a 25Way D "test" connector I made up. All readings were no where near zero. I found that if I connected mains earth to the ground inputs on the test connector then Channels 1 through 5 and 14 through 19 all showed zero whilst channels 6 through 13 and 20 through 22 all showed full scale.
On the ADC 16s, testing in a similar manner also showed that mains earth is needed on the ground inputs before the readings were correct.
Borth the ADC 16s are connected to the computer via a USB to RS232 port expander and the ADC 22 is connected via your USB to parallel adaptor.
What is going on?
I await your response.