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Problems of the reading jump of the thermocouples

Hi,
I am a new user of Datataker DT85. Some of the thermocouple readings show a large instant jumping up (about 1~3°C) which is unreasonable and groundless although I do not change anything.

Also, when I turn on the humidity sensor power supply, the readings of the thermocouples are jumping about 10 °C.
Could you help give some advice about this problem? Many thanks.

Regards,
Siyuan

Hi, I am a new user of Datataker DT85. Some of the thermocouple readings show a large instant jumping up (about 1~3°C) which is unreasonable and groundless although I do not change anything. Also, when I turn on the humidity sensor power supply, the readings of the thermocouples are jumping about 10 °C. Could you help give some advice about this problem? Many thanks. Regards, Siyuan

Hi Siyun,

Could u please provide log file , and sensors type or model , and connection details to understand the issue better.

With Regards,

RRN

Hi Siyun, Could u please provide log file , and sensors type or model , and connection details to understand the issue better. With Regards, RRN

Best regards, DataTaker Team (RRN) Thermo Fisher Scientific www.thermofisher.com.au

Hi,

The thermocouple is Mineral Insulated Thermocouple Sensor (T type) with M8 x 2mm Threaded Pot Seal from Thermosense company. It seems to show large jumping when I turn on the centrifugal fan, could you provide any methods to solve this problem?
626a8280e4220

Kind regards,
Siyuan

Hi, The thermocouple is Mineral Insulated Thermocouple Sensor (T type) with M8 x 2mm Threaded Pot Seal from Thermosense company. It seems to show large jumping when I turn on the centrifugal fan, could you provide any methods to solve this problem? ![626a8280e4220](serve/attachment&path=626a8280e4220) Kind regards, Siyuan

Hi,

When the DT85 datalogger is plugged with only one channel of thermocouples, I turn on the centrifugal fan and it will not jump up immediately. But the readings will jump up after about 10 min.

Siyuan

Hi, When the DT85 datalogger is plugged with only one channel of thermocouples, I turn on the centrifugal fan and it will not jump up immediately. But the readings will jump up after about 10 min. Siyuan

Hi Siyun,

1) this could be due to the Temperature Variations Around the Reference Junction Connection, So please make sure no fans or other sources of cooling or heating are located near the reference junction

Simple insulation can also protect the junctions from extreme temperatures

2)Doublecheck the connection and, if necessary, swap the thermocouple lead wires

With Regards,
RRN

Hi Siyun, 1) this could be due to the Temperature Variations Around the Reference Junction Connection, So please make sure no fans or other sources of cooling or heating are located near the reference junction Simple insulation can also protect the junctions from extreme temperatures 2)Doublecheck the connection and, if necessary, swap the thermocouple lead wires With Regards, RRN

Best regards, DataTaker Team (RRN) Thermo Fisher Scientific www.thermofisher.com.au

Hi Siyuan and Raj,

It is a bit tricky to read thermocouples when you have an external electromagnetic interference. @rajreddynalbal is correct, you can remove the fan for a fast solution as it created an interference (switch ON/OFF) which then turn into a signal that disrupts the reading.

Or you can isolate the logger power supply from the one used by the fan (an external 12V battery could be a good replacement), then twist the thermocouple cable to reduce the interference.

If you connect the thermocouple between + and - pin, you can connect the - pin to AGND to ground the thermocouple. You can check either one of them or all of them should be used in your system.

Best regards,
dataTaker Expert

Hi Siyuan and Raj, It is a bit tricky to read thermocouples when you have an external electromagnetic interference. @rajreddynalbal is correct, you can remove the fan for a fast solution as it created an interference (switch ON/OFF) which then turn into a signal that disrupts the reading. Or you can isolate the logger power supply from the one used by the fan (an external 12V battery could be a good replacement), then twist the thermocouple cable to reduce the interference. If you connect the thermocouple between + and - pin, you can connect the - pin to AGND to ground the thermocouple. You can check either one of them or all of them should be used in your system. Best regards, dataTaker Expert

Hi,

I try to put the datalogger inside a metal box and increase the distance between the datalogger and fan. However, the reading problem still happens. Could you help arrange an engineer to our lab If it is possible? What's the price of this kind service?

Best regards,
Siyuan

Hi, I try to put the datalogger inside a metal box and increase the distance between the datalogger and fan. However, the reading problem still happens. Could you help arrange an engineer to our lab If it is possible? What's the price of this kind service? Best regards, Siyuan

Hi Siyuan,

What is the out put of the Thermocouple sensor?
Is it possible to monitor(with scope or something) and confirm if this is a stable one?

Best Regards,
BR

Hi Siyuan, What is the out put of the Thermocouple sensor? Is it possible to monitor(with scope or something) and confirm if this is a stable one? Best Regards, BR

Hi Siyuan,

The part that needs protection is not the logger but the wire between the logger and the sensor tip. This cable can pick up electromagnetic interference, even with a small 1 mV difference can cause a 5 degC offset.

Therefore I recommend you twist the thermocouple wire or slide the wire through a small metal pipe (similar to use a thermocouple wire with shield).

Best regards,
dataTaker Expert

Hi Siyuan, The part that needs protection is not the logger but the wire between the logger and the sensor tip. This cable can pick up electromagnetic interference, even with a small 1 mV difference can cause a 5 degC offset. Therefore I recommend you twist the thermocouple wire or slide the wire through a small metal pipe (similar to use a thermocouple wire with shield). Best regards, dataTaker Expert
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