Siemens sitrans tr200, Operating Instructions Manual

Page: 28 / 78

Connecting
5.5 Notes on measuring current
SITRANS TR200/TR300
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Operating Instructions, 04/2007, A5E01071992-01
5.5 Notes on measuring current
If you use the transmitter for measuring current, connect an external measuring resistor R
across the transmitter connection terminals 5 and 6. The transmitter uses this resistor to
perform the required current measurement as a voltage measurement. Therefore, the
following instructions must be complied with in the parameter assignment software
SIPROM T for SITRANS TR200 and SIMATIC PDM or HART communicator for
SITRANS TR300:
●
Sensor class selection = Millivolt transmitter
● Process value scale: Multiply each of the start of scale value and end of scale value for
desired current range with the value of the resistor R that is connected externally across
terminals 5 and 6 of the transmitter.
● Example: Measurement of a 0 to 20 mA current via an external resistor R of 10 Ohm
sensor class = millivolt transmitter
process value scale:
–
Start of scale value = 0 mA ⋅ 10 Ω = 0 mV
–
Full scale value = 20 mA ⋅ 10 Ω = 200 mV
The 4 to 20 mA output current now follows the profile of the sensor input, i.e. the 0 to 20
mA current signal.
If during current measurement the measured values are called up via the digital interface,
such as HART for SITRANS TR300, the measurement data are shown in the operating
software as voltage signals mV units. The voltage signals are scaled by the factor of the
externally connected resistance value R.