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Which kind of Thermocouple sensor can we use with TM3xx/TMC2xx/TMC4xx analog I/O modules and cartridge

Published date: 11 December 2018

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 .

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