Hi to all I was told by SIEMENS that the analog input module doesn't have this facility. It needs to be done by the application software. Isn't that strange? They told me the thermocouple modules DO detect open circuit... Thanks in advance ! Eduardo.
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
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