Omega OMB-DAQBOARD-500 Differential for Floating Signal Sources, Resistor Connection Scenarios

Differential for Floating Signal Sources

Floating Signal Sources are typically wired to a data acquisition board in Single-Ended configuration. However, when the Floating Source signal leads pass through an electrically noisy environment, Differential configuration will give the best performance.

When wiring Floating Signal sources in Differential configuration, a resistor can be connected from the low side of the sources to analog ground (AGND). These resistors create a return path to AGND for the bias currents of the instrumentation amplifier and can reduce the common mode noise.

All DaqBoard/500 Series boards provide 10 MΩ of resistance between each analog input and ground. In most cases the 10 MΩ of resistance is sufficient for the return of bias current.

Resistor Connection Scenarios

If the Input Signal is DC Coupled

Use a Resistor Value from: 10 KΩ to 100 KΩ Connect the resistor between:

Input Signal Return (ARET) and AGND

If the Input Signal is AC Coupled

Use resistors with values from: 10 KΩ to 100 KΩ

(a) Connect one resistor between:

Input Signal High and Input Signal Low

(b)Connect a second resistor between: Input Signal Low and AGND

Making resistor connections as indicated will significantly increase the load on the measurement source, possibly reducing the measured voltage. A trial and error approach may be required when trying to reduce common mode noise.

The following figure shows how to properly wire a Floating Source Signal in Differential configuration.

Differential Configuration for Floating Sources

2-10 Connections & Pinouts 887293 DaqBoard/500 Series User’s Manual