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Temperature transmitters

What are 2-, 3- and 4-wire circuits?

They describe the number of wires with which the measuring resistor (e.g. a Pt100) is connected. While with the simplest 2-wire connection, the lead resistance can falsify the measuring result, this negative influence can be compensated within the 3- or 4-wire connection, and thus the accuracy of the measurement improved.

What are Profibus / FOUNDATION Fieldbus?

Profibus / FOUNDATION fieldbus are digital output signal protocols.

What are the signalling values in accordance with NAMUR?

NAMUR Downscale: 3.5 mA
NAMUR Upscale: 21.5 mA

What are the special features of the T32 SIL transmitter?

It has had a FMEDA analysis carried out on it. The T32 has been developed in accordance with IEC 61508 and has been manufactured accordingly. The T32 operates exclusively with active write protection.

What do "output limits" mean?

Up to these signal limits, a measuring signal is generated.

What does „Pt100“ mean?

Pt stands for Platinum with a nominal resistance of 100 Ohm at 0 °C (EN 60751).

What does 'SIL' mean?

SIL (Safety Integrity Level) refers to the standards IEC61508 / IEC61511 and describes instruments, which are used for safety-critical applications. In the event of an emergency, they must react safely and place the control circuit into a safe state.
On these grounds, all components in the control circuit (sensor, logic, actuator) must have a SIL classification.
The control circuit (safety loop), through special parameters (SFF, PFD, FIT), can have its Failure Probability evaluated.

What happens with a high ambient temperature > 85 °C?

High TC error and damage to the electronic components.

What is 'signalling'?

The signalling shows possible error conditions (e.g. sensor burn-out).

What is galvanic isolation?

An isolation of the signal between the signal side and the output side (e.g. through coils).

What is the difference between analogue and digital transmitters?

At WIKA, analogue transmitters have analogue electronics fitted but no processors.
Digital transmitters have processors. The output signal can, however, be a 4 ... 20 mA analogue signal for both types.

What is the value of the current at the output limits in accordance with NAMUR?

Lower output limit in accordance with NAMUR is 3.8 mA (other value possible)
Upper output limit in accordance with NAMUR is 20.5 mA  (other value possible)

What should be considered when measuring level with transmitters (potentiometers)?

Pure percent measurement (ratio measurement)
T32: amplifier adjusted to input 10 kΩ to 100 kΩ
Smaller values are measurable, but with less accuracy.

What should be considered when measuring temperature with thermocouples?

For temperature measurement using thermocouples, a reference value is always needed and/or a compensation must be made. Thus, there is a sensor built into the digital transmitter (Pt100) which measures the terminal temperature (ambient temperature). (cold junction, CJC, cold junction compensation).
Thermocouple connection is always 2-wire. (Caution: do not swap over the plus and minus!)
No sensor short circuit monitoring is available (only sensor break monitoring)
Transmitters with galvanic isolation are strongly recommended (WIKA Models T12, T32, T53).