FP-AI-110 Multiple Channels - Signal Degredation

[RVallieu]

We have a FP-AI-110 set up with a FP-PS-4 and communicating back over a FP-1000.  Set-up to read Current. -21 to 21mA

I had a customer ask if connecting more than one signal input line to the AI-110 would cause signal loss on the multiple channels, getting worse with the more channels that are connected.

Is this a concern with this module?

[RVallieu]

The above is incorrect, I was getting questions through a second non-technical party trying to translate....

They really wanted to know the input resistance on the channels that causes the voltage drop for the current sensing, and what the minimum voltage would be.  I see from the literature that it is 100 Ohms resistance on the inputs.

But then I see later in the operations manual that it lists 60-150 Ohms.....which is correct?

Current Inputs

Input impedance................................60–150 Ohm

[Hal_L]

Hi,

The 60-150 Ohm specification is the correct one. I am going to make sure that this old 100 Ohm specification is updated on the data sheet. Thank you for pointing that out.

Regards,
Hal L.

[RVallieu]

Does it switch resistance based on channel range?

How do you select what value to use?

[Hal_L · Accepted solution]

Hi,

So the AI-110 was rev'd recently, and we added additional input protection. In the new revisions, the old 100 Ohm resistor was replaced with a thermistor to add additional input protection.

The thermistor's resistance changes value with temperature, so if someone applies too much voltage, the resistance will go up and protect the input. The thermistor helps protect the FP-AI-110 from damaging voltages.

Regards,

Hal L.