Temperature transmiter with PT100

joaco1993

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Sep 2014
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newyork
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Im having a 3wire pt100 connected to a temperature transmiter. Im reading the current in the loop and I have 22mA, so is overrange.

What could cause this meassure ?? Surely the pt100 is "broken", but what could be broken ? shortcircuit ? open wire ?

It should be shorcircuit right ?

Thanks!

pd: i dont have the sensor here, so i cant meassure the resistances between the wires..
 
3 wire sensors are usually colour coded 2 red & 1white the 2 reds go to the two terminals that are shown on the diagram as connected to the same point on the sensor diagram and white to the other, a current of 22ma seems to indicate that the PT100 is Open circuit. Try a 100 ohm resistor across and link what would be the terminals that show the two reds. this should show around 0 Deg. C. Just a thought the transmitter may be configured to show max if a short is detected, this is usually to protect the process if heating mode.

3-wire-Pt100-diagram.jpg
 
3 wire sensors are usually colour coded 2 red & 1white the 2 reds go to the two terminals that are shown on the diagram as connected to the same point on the sensor diagram and white to the other, a current of 22ma seems to indicate that the PT100 is Open circuit. Try a 100 ohm resistor across and link what would be the terminals that show the two reds. this should show around 0 Deg. C. Just a thought the transmitter may be configured to show max if a short is detected, this is usually to protect the process if heating mode.

The 100ohm resistor should go between red and white, not red and red.
 
If the intensity at the transmitter output is 22mA, there is surely a problem with the sensor, either short-circuited or open or wrong connected.

The temperature transmitters are designed so if the sensor fails the output goes to maximum then the heaters are turned off and an over temperature does not occur.
 
With 3 wires there 6 wiring combinations, only two of which will work.



Highest probability: it's mis-wired.
 
The temperature transmitters are designed so if the sensor fails the output goes to maximum then the heaters are turned off and an over temperature does not occur.

Many programmable ones let you choose what to do in the case of fault. Whilst they should be configured as you mentioned, I've seen the opposite in the past... just something to be aware of when getting the programmable type.
 

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