Temperature measurement under strong electromagnetic fields

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avillegas
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Joined: Tue Aug 27, 2019 2:09 pm

Temperature measurement under strong electromagnetic fields

Post by avillegas » Tue Aug 27, 2019 2:27 pm

Hi,
I'm working on an application requiring 4 temperature measurement points in the presence of a very strong electromagnetic field coming from a wireless power transmission system ( operating in a frequency minor to 250 Khz). I need to log data for at least 8 hours and take measurements every 10 ms at least. Resolution should be under 0.1 oC in a range from 20oC to 60oC.
Could you recommend which of your products may be suitable for this?

Regards

Gerry
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Posts: 494
Joined: Mon Aug 11, 2014 11:14 am

Re: Temperature measurement under strong electromagnetic fields

Post by Gerry » Thu Aug 29, 2019 11:14 am

Hi avillegas,

Unfortunately we have no off-the-shelf solution, for your specific application, but we do have a partial solutions that you could add required components to. So, in order to retain the accuracy by minimizing the effects of the high electromagnetic field you would need to use a method described below (or suitable alternative):

The most suitable product that we have would be a PT-104 data logger, which has a temperature accuracy of 0.015 °C + 0.01% of reading (see here: https://www.picotech.com/data-logger/pt-104/pt-104-specifications), with a PT100 probe that is most suitable for what you will be measuring the temperature of, (i.e. air, liquid, solid, etc) from our range of probes (see here: https://www.picotech.com/data-logger/pt-104/pt-104-accessories#tab_pt100-sensors).

For minimizing the interference, you could either shield the temperature data logger and use a short RTD sensor cable in a Faraday Cage, or use an RTD sensor with longer cabling and an effective high field strength cable shield conduit along with the Faraday Cage for the temperature data logger. There are a number of manufacturers of Faraday Cages, that you can find on the internet that may be able to provide you with what you need, but a manufacturer of a suitable conduit in a very small quantity is not going to be easy to find.

If you were able to relax your requirement to 60ms intervals, you could use a high precision high accuracy general purpose data logger such as our ADC-20 (see here: https://www.picotech.com/data-logger/adc-20-adc-24/precision-data-acquisition), again with a Faraday Cage, and a high accuracy thermistor, with relatively short cabling connected to 2 inputs of the ADC-24 differentially (or using a 4-wire connection to minimize the error due to the resistance of long cabling, connected to 2 pairs of inputs differentially) with the cabling using twisted pairs.

Alternatively, you could use a high accuracy temperature sensor that provides a 4-20mA loop current output, on a twisted pair cable, and connect it across a shunt resistor placed on the Terminal board (see here: https://www.picotech.com/accessories/miscellaneous/adc-20-24-terminal-board) at a single-ended input of the ADC-20 (again in a Faraday Cage) as the comparatively higher current flow with negative and positive direction in the closely coupled cable would provide high immunity to induced interference.

The 3rd solution would be the easiest to implement (if you can find a suitable temperature sensor) and using a 4-20mA sensor output is common practice in applications where there are high levels of interference such as industrial machine shops. For all of the solutions, you would use our PicoLog 6 software (see here: https://www.picotech.com/library/data-loggers/picolog-6-data-logger-software) which would satisfy your logging requirements, and if you can't relax your requirement to 60ms intervals then at least you have more possible methods that you may be able to apply elsewhere.

Regards,

Gerry
Gerry
Technical Specialist

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