Analog Input Koyo

I have an analog input card F4-08AD.
It's on a D4-430 CPU.
What I was noticing is that the voltage between CH 2COM and CH2 IN creeps up slowly .
When I go online I can see the creep.
The thing is I notice that all of the Inputs do this when they are not connected to a load.

When I put a tester accross to check the voltage, I can see the voltage at up to 16V, but it starts dropping immediately once I begin measuring.
The V3002 value drops from 4095 down until I remove the leads.
When I look at the V3002 value it begins to creep up again.
Is this normal?
Thanks for any comments.

It sounds like it's floating. If it stays still when you put a signal in then it's OK. Go online and see if the register reads your input correctly. Put in 0%, 50% and 100%.

Yes It stays put when I put say 5 volts to it. V number doesn't budge.
I just never noticed the way the potential between the two terminals raised up like that when there is no load.
Thanks for the reply.

Voltage creep is normal for this module when the inputs are floating.

This is not an uncommon problem for some types of analog inputs, particularly if they are multiplexed (and just about all PLC's and PC's use multiplexed input modules). Another characteristic is that if you have a group of unused channels in sequence, they will all read approximately the same 'bogus' value.

Usually it is caused by high impedance of a voltage input channel and/or stray capacitance. When you connect a voltmeter across the terminals, your meter adds just enough load to that channel to counter-act this effect. This is why you might see one value before you connect a meter and the 'real' value after you connect a meter.

It is generally a good practice to tie unused analog input leads together to insure zero volts at the terminals if this is a problem, but typically this is just a cosmetic issue and most people choose to ignore unused channels. Another solution (if available) is if the module uses switches to configure for voltage or current input, set the unused channel for current input. This will generally put a low impedance resistor (250-500ohm) across the input channel. I usually wire unused channels to terminal blocks for future use, and then add a jumper across the terminals and add a WELL DOCUMENTED NOTE ON THE DRAWINGS!!!! as to why the jumper is there.

Greg as always you nailed it.
I was having one of those intermittent problems. (the Kind I love)
The problem was a badly frayed cable coming from a Temposonic transducer to the analog input card.
The power feed must have been crossing the signal line and sending the high voltage to the analog card.
I would disconnect the input lines and see that the V3002 value didn't change.
Anyhow the problem is fixed now.
Thanks for the input.
George Bradley