S7-200 auto detects broken 4-20 mA current loop ?

Which particular Siemens card are you talking about ?

Broken Sensor Protection on thermocouple circuits has long since been a feature of most systems, presumably because of their tendancy to fail and the need to create an alarm or trip. It is normally done via a separate monitoring signal that causes the signal to go hard to top or bottom of the scale depending on the application.

Steve

snipped-for-privacy@gmail.com wrote:

If a 4-20mA analogue input is 0 or 25mA the sensor is broken

If you really want a seperate alarm then put in a trip amplifier

Not necessarily, 0mA could imply open circuit cabling, 25mA could mean a short circuit.

Also some intelligent transmitters can be configured to fix the output current at specific current levels corresponding to detected faults, ie a broken thermocouple in the case of a temperature transmitter. The system is then programmed to display specific error messages.

Steve

Yes, The statement 'the sensor is broken' is a bit of a generalisation from the sensors POV

'the sensor loop is broken' is better...I meant to imply that 0 and +24mA are common and easily detectable fault conditions in an analogue loop...for which the cabling is the most likely culprit

Now that would be handy