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imc C-SERIES - Manual, Version 4 R 3 - 2018-10-19

15Grounding with power supplied by a car battery

2.7 Grounding with power supplied by a car battery

imc CL Devices with isolated DC-supply (e.g. battery)

If the power supply (e.g. car battery) and the measurement device are at different voltage levels, then if

they were connected by the supply line, it would cause a ground loop. For such cases, the isolated

internal device power supply ensures separation of the two voltage levels. The ground reference for the

measurement device must then be established in a separate step.

For running on an isolated DC power supply source (e.g. battery), either the grounding socket terminal, a

grounding contact on the device ("CHASSIS"), or the CHASSIS contact on the imc signal connectors must

be used.

Isolated power inputs avoids ground loops in distributed topologies

With stationary installations and the use of (already isolated) AC/DC adapters, any system ground

differentials between the device and the central or local power supplies may not be relevant. The big

issue in such a case, in contrast to mobile, in-vehicle applications, is from where to obtain a reliable

ground voltage. Since it is convenient to use the AC power supply’s protection ground line as the ground

voltage, the LEMO-terminated AC/DC adapters for imc measurement devices are designed so that the

protection ground line is connected all the way through to the LEMO connector’s housing, thus securing

the device’s voltage level to protection ground. Additionally, in the AC/DC-adapter’s LEMO-terminal (not

the device’s LEMO-socket!), the reference ground of the power adapter is connected with the housing’s

(CHASSIS) protection ground: Since the AC/DC power adapter is already isolating, as is the power input,

this supply voltage’s reference would not initially be defined and can be set arbitrarily. In particular for

reasons of suppressing HF (high-frequency) interference signals stemming from the AC/DC switching

power adapter, direct grounding is normally advisable.

2.8 Shielding

Also, all signal leads to the device must be shielded and the shielding grounded (electric contact between

the shielding and the plug housing "CHASSIS").

To avoid compensation currents, always connect the shielding to one side (potential) only.If the imc

DSUB block screw terminal plug is used, the shielding should be connected to the pull-relief clamp on the

cable bushing. This part of the conductor-coated plastic plug housing has electrical contact to the device's

housing, just as Terminals 15 and 16 (labeled: "CHASSIS", to the left and right of the imc-plug cable

bushing) do; but is preferable to the "CHASSIS" terminals for optimum shielding.

IMC C SERIES User Manual

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