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

98 Device description

5.6.2.2 PT100 (RTD) - Measurement

Along with thermocouples, PT100 sensors can also

be connected, in 4-wire configuration. An extra

reference current source feeds an entire chain of

up to four serially connected sensors.

The imc-thermo plugs (ACC/DSUBM-T4) has 4

contacts which are available for the purpose of 4-

wire measurements. These current-supply contacts

are internally wired so that the reference current

loop is automatically closed when all four PT100

units are connected. This means that the –I contact

of one channel is connected to the +I contact of

the next channel (see the sketch imc thermo

plug ). Therefore, for channels not connected to

a PT100 sensor, a wire jumper must be used to

connect the respective "+Ix" and "-Ix" contacts.

Normal DSUB-15 connectors don't come with these extra "auxiliary contacts" for 4-wire connections. This

means that you must take steps to ensure that the reference current flows through all PT100 units. Only

"+I1" (DSUB(9), Terminal K1, "(RES.)") and "–I4" (DSUB(6), Terminal K10, "(GND)") are available as a

contact or DSUB-15 pin, respectively. The connections "–I1 = +I2", "–I2 = +I3", and "–I3 = +I4" must be

wired externally.

PT100 sensors are fed from the module and don’t have or even require an arbitrarily adjustable

reference voltage in the sense of an externally imposed common mode voltage. It is also not permissible

to set one up, for instance by grounding one of the four connection cables: the PT100 reference current

source is referenced to the device’s frame (CHASSIS), and is thus not isolated.

5.6.3 Current fed sensors

At the connection sockets, a permanent 5 V supply voltage for external sensors or for the ICP

expansion plugs ACC/DSUB-ICP and ACC/DSUB-ICP2-BNC is available. This voltage source is

grounded to the measurement device's frame.

The description of measurement with ICP sensors is presented here.

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IMC C SERIES User Manual

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