Zonge GDP-32 - Field Configurations

TIME DOMAIN INDUCED POLARIZATION (TDIP)
Section 9, Page 19 May 2002
9.7 FIELD CONFIGURATIONS
Be very careful when running a multiple channel receiver to avoid common mode problems.
Common mode effects are caused by lack of a reference voltage or level (floating ground), or a
reference level that exceeds common mode limits of the input amplifiers.
The maximum permissible common mode levels for the standard configuration of the GDP-32
II
is r10 volts. With isolation amplifiers, this level can extend to several thousand volts, but the
tradeoff is higher noise and lower overall frequency response.
The best configuration that we have found is to install a standard copper/copper-sulfate
Reference Electrode (or equivalent) connected to both analog ground (COM on the analog side-
panel) and the case ground (CASE GND on the side panel). Place the electrode next to the
receiver and at least two meters from the nearest receiving electrode. This also provides
maximum protection from static discharge and nearby lightning strikes.
Additional protection in lightning-prone areas can be gained by using a galvanized iron plate (or
equivalent) as a reference electrode. This plate should be buried close to the receiver in a hole
that has been well watered and the soil mixed to make good mud contact with the plate. Typical
size for the plate would be 30 cm by 30 cm.
The following figures provide examples of receiver connections using the Reference Electrode or
Reference Pot connected to both analog ground (COM) and case ground (CASE GND).
To obtain the best noise rejection, Zonge Engineering recommends connecting the analog ground
(COM) to the case ground (CASE GND) on the analog I/O side panel.
NOTE: The GDP-32
II
receiver has a captive jumper between COM and CASE GND for the
standard configuration.