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Which kind of Thermocouple sensor can we use with TM3xx/TMC2xx/TMC4xx analog I/O modules and cartridge
Thermocouple category definition
It exists two main categories of thermocouple sensors
1) “Isolated “ or “ungrounded” thermocouple : the 2 wires junction is insulated from the Metalic part of the sensor and so from the shield (present all around and along the sensor’s cable )
2) “grounded” or “non isolated” thermocouple : the 2 wires junction is connected to the metallic part , and so indirectly connected to the shield all around and along the thermocouple cable
Within the TMC2TI2 cartridge and TM3TI4x, TM3TI8Tx, TM3TM3x modules it’s advised to use exclusively “isolated” thermocouples ( and not a “grounded thermocouple)
else when more than one sensor is connected onto different channel of one such module, the result is wrong temperature measurements for all the channels
Deeper explanation :inside the TMC2TI2/TM3xx all their channel inputs pins named Ix- (with x =0,1,2,3,4 to n, n number of analog channel supported by the module) are all internally connected together , as soon as 2 “grounded” thermocouple sensors are connected to the same module/cartridge, (same way all sensors would have been mounted in parallel onto the same channel input) , this would provide wrong temperature measurements, by giving nearly same temperature measurements values for all the sensors inputs what ever real temperature on each sensor !
Only with TMC4TI2 cartridge , it’s possible to used both “isolated” or “grounded” kind of thermocouple sensors .
There is no restriction because TMC4TI2 channel inputs pins I0- and I1- are non connected internally, they are isolated .
It exists two main categories of thermocouple sensors
1) “Isolated “ or “ungrounded” thermocouple : the 2 wires junction is insulated from the Metalic part of the sensor and so from the shield (present all around and along the sensor’s cable )
2) “grounded” or “non isolated” thermocouple : the 2 wires junction is connected to the metallic part , and so indirectly connected to the shield all around and along the thermocouple cable
Within the TMC2TI2 cartridge and TM3TI4x, TM3TI8Tx, TM3TM3x modules it’s advised to use exclusively “isolated” thermocouples ( and not a “grounded thermocouple)
else when more than one sensor is connected onto different channel of one such module, the result is wrong temperature measurements for all the channels
Deeper explanation :inside the TMC2TI2/TM3xx all their channel inputs pins named Ix- (with x =0,1,2,3,4 to n, n number of analog channel supported by the module) are all internally connected together , as soon as 2 “grounded” thermocouple sensors are connected to the same module/cartridge, (same way all sensors would have been mounted in parallel onto the same channel input) , this would provide wrong temperature measurements, by giving nearly same temperature measurements values for all the sensors inputs what ever real temperature on each sensor !
Only with TMC4TI2 cartridge , it’s possible to used both “isolated” or “grounded” kind of thermocouple sensors .
There is no restriction because TMC4TI2 channel inputs pins I0- and I1- are non connected internally, they are isolated .
Released for:Schneider Electric UK
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