pseudo-differential inputs

[SolarRon]

On the use of pseudo-differential inputs such as on the PCI-6110, various references say that the (-) input should not vary "much" with time.
Does anyone know how "much" it can vary? Presumably 60Hz is OK. Does it have a frequency response specification?
How much error is introduced by using it as if it were the negative input of a truly differential signal? When is
it necessary to use the difference between two input channels in order to obtain accurate differential signals?

[LA 75]

Hello,

The 6110’s analog input is pseudo differential in that the positive input measures the signal of interest and the negative input is the ground reference (signal return path). The negative input helps in reducing the effects of low frequency common-mode noise. The common-mode voltage must be within ±11 V of the 6110 AIGND voltage, which is essentially the local earth (chassis) ground of the computer.

Pseudodifferential has a capacitor conected between CH 0- and ACH0GND. Differential is a better choice than pseudodifferential, but pseudodifferential works fairly well for a variety of applications. For DC voltage applications and low frequencies, pseudodifferential works perfectly. For higher frequencies, you should take into consideration that this capacitor is going to look like a short circuit, so CH 0- and ACH0GND are going to be the same point.

Hope this helps,

LA