IMC CANSAS - Voltage Measurement; Voltage Source with Ground Reference; Voltage Source Without Ground Reference

To Next Page

To Previous Page

298 Properties of the Modules

6.7.2 Voltage measurement

Voltage: ±10 V to ±5 mV in 9 different ranges

The input impedance is 20 M . (1 M when switched off)

6.7.2.1 Voltage source with ground reference

The voltage source itself already has a connection to the device’s

ground. The potential difference between the voltage source and

the device ground must be fixed.

Example: The device is grounded. Thus, the input -VB (D) is also at

ground potential. If the voltage source itself is also grounded, it's

referenced to the device ground. It doesn't matter if the ground

potential at the voltage source is slightly different from that of the

device itself. But the maximum allowed common mode voltage

must not be exceeded.

Important: In this case, the negative signal input -in (B) may not be

connected with the device ground -VB (D). Connecting them would

cause a ground loop through which interference could be coupled

in.

In this case, a genuine differential (but not isolated!) measurement

is carried out.

6.7.2.2 Voltage source without ground reference

The voltage source itself is not referenced to the device ground

but is instead isolated from it. In this case, a ground reference

must be established. One way to do this is to ground the voltage

source itself. Then it is possible to proceed as for "Voltage source

with ground reference". Here, too, the measurement is

differential. It is also possible to make a connection between the

negative signal input and the device ground, in other words to

connect -in(B) and -VB(D).

Example: An ungrounded voltage source is measured, for instance

a battery whose contacts have no connection to ground. The

module is grounded.

Important: If -in(B) and -VB(D) are connected, care must be taken

that the potential difference between the signal source and the

device doesn't cause a significant compensation current. If the

source's potential can't be adjusted (because it has a fixed,

overlooked reference), there is a danger of damaging or destroying

the amplifier. If -in(B) and D are connected, then in practice a

single-ended measurement is performed. This is no problem if

there was no ground reference beforehand.

Other manuals for IMC CANSAS