Voltage in DO818 without charge
This is our first commissioning of the Compact Hardware with DO818 with TU818.
When we measure voltage between terminals L- and CH in TU818 termination without the DO818, the voltage is "zero". It's right.
But when we install the DO818 in this TU818, without charge it (terminals opened), the voltage is 17 Volts. It must be “zero” Volts.
When we charge it (closed terminals) the voltage is shown 24 Volts. It is right.
Most probably 17V is the voltage without any load., connected to the output.
And that is not wrong in case of transistor output, the voltmeter usually have a high input resistance and could not create a load (current).
You have to connect a load - relay, lamp or resitor between Ch and L-, and then to check the voltage again.
You can explain that techicians that they don't need to measure output voltage in order to check 0 or 1 to the output - instead they can look at the LED for each channel. It defenitelly shows the status of the output.
Anyhow, you always have a load, connected to the output (relay, lamp e.t.c.). In this case I beleive voltage at output terminals will be 0V.
Could you please check if 24VDC is correctly connected to the module (TU...) - these are terminals L1+/L2+ and L1-/L2-, because the outputs are divided in 2 groups.
In case you don't want to have this leakage current (resp. no-load voltage), you have to select relay outputs with dry contact.
All this above you can find in the attached document