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5.5
Notes on measuring current
Connect an external measuring resistor R to the transmitter connection terminals 5 and 6 if
the transmitter is used for measuring current. 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 parameterization software SIPROM T with
SITRANS TH200 and SIMATIC PDM or HART communicator with SITRANS TH300:
● Sensor class selection = Millivolt transmitter
● Process value scale: Multiply the both the start of the scale value and the full scale value
● Example: Measurement of a 0 to 20 mA current via an external resistance R of 10 Ohm
If, for a current measurement, the measured values are called up via the digital interface,
e.g. HART with SITRANS TH300, then the operating software displays the measurement
data as a voltage signal in the unit mV. The voltage signal is scaled by the factor of the
externally connected resistance value R.
5.6
Test terminals for output signal
The "Test +" and "Test -" test terminals are used for checking the 4 to 20mA current with an
amperemeter. The voltage drop across the amperemeter must not exceed 0.4V for a 23mA
output current.
SITRANS TH200/TH300
Operating Instructions, 06/2010, A5E00393069-03
of the required current range with the resistance value R, which is connected externally to
terminals 5 and 6 of the transmitter.
Sensor class = Millivolt transmitter
Process value scale:
Start of scale value
–
Full scale value
20 mA ⋅ 10 Ω
–
=
The 4 to 20 mA output current now follows the profile of the sensor input, the 0 to 20 mA
current signal.
0 mA ⋅ 10 Ω
0 mV
=
=
200 mV
=
Connecting
5.5 Notes on measuring current
29
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