
ZENO
®
-3200 USER MANUAL
Coastal Environmental Systems (206) 682-6048
Page 243
Sensor ground (marked SGND): this ground should be used only for sensitive, single-ended sensors.
Typically, sensors with a full scale voltage less than 50 mV and source impedance greater than 10 k
would be suitable for SGND. No harm will be caused by grounding less sensitive sensors to SGND;
however, sensors returning greater currents through SGND may disturb those returning smaller
currents.
13.3. CONNECTING DIFFERENTIAL INPUTS
Connecting the ZENO
®
-3200 inputs in differential mode is usually done only with sensors that are
inherently ground-referenced. The following bridge circuit is an example of this.
Figure 13-2. Connecting a Differential Circuit with Excitation Voltage.
When making a differential measurement using a sensor or source that is not ground-referenced you must
provide a return path for the leakage currents. If this path is not provided, those currents will charge stray
capacitances, causing the output to drift uncontrollably or to saturate. There are several ways to provide
this path, depending on the output configuration of the source/sensor being measured.
®
EXC+
CH+
CH-
AGND
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