Author Topic: TM-902C: cheapest dedicated k-type thermocouple thermometer review  (Read 3995 times)

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Offline electronupdate

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So I was getting tired of having to move my multimeter around to measure temperature at various point of a prototype I am working on.  The solution, of course, would be a thermal camera.... but they are still too expensive.

The next best thing would be some dedicated meters which would accept standard k-type thermocouples.  A quick web search shows up the "TM-902C" as the go-to meter at the bottom end.  Wonderfully uncomplicated (there is only a power switch), it works as advertised.

It would have been nice, however, if there was a way to calibrate the meters.  One of them is different than the other 3 (still within spec from what I can tell).. the PCB hints at test points for calibration and switching between fahrenheit and celsius modes  however, there is no documentation.


Offline mariush

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Re: TM-902C: cheapest dedicated k-type thermocouple thermometer review
« Reply #1 on: April 26, 2014, 12:25:48 am »
Like a video comment says, those thermocouples can only do 250-450c ... the isolation on the cable and the blob in the tip can't handle much higher temperatures.

For 1100c you need probes that cost 15-30$ a piece, or even more. For example see this one, with stainless steel, insulated sheath etc etc : 

Online Vgkid

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Re: TM-902C: cheapest dedicated k-type thermocouple thermometer review
« Reply #2 on: April 26, 2014, 02:21:27 am »
Thanks for the review, I'm comtemplating getting one of these.
If you own any North Hills Electronics gear, message me. L&N Fan

Offline Gyro

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Re: TM-902C: cheapest dedicated k-type thermocouple thermometer review
« Reply #3 on: April 04, 2015, 11:09:21 pm »

Sorry to resurrect an old topic, but given that these things are still available so cheaply on ebay I though it was worth it.

Only my second post, I've been lurking as a guest for a while but thought I would wait until I had something to say.

Anyway I purchased one of these a while back from a UK seller. On inserting the battery I was greeted by a burning smell and rapidly heating battery. I contacted the seller and apparently I was one of several. After receiving a refund threw it into a dark corner. A few weeks later I decided to investigate. It was immediately clear that the SOT223 3V regulator on the board was blown and the source of the smell. No idea why, it should have been well within voltage rating and I hadn't reversed the battery. Probably a case of 'contents not matching the label'. Curiously the power switch was wired AFTER the regulator too, meaning low continuous quiescent drain on the battery.

I removed the regulator and bridged the footprint and powered the rest of the circuit from a bench supply and found that it was quite happy. What's more it was quite happy down to about 1.6V, ie. end voltage of a pair of 1.5V cells, when the low battery indicator came on! There was no change in display over the normal expected voltage range.

I have no idea of the logic of powering a chip designed for 3V operation from a 9V battery via a non-zero cost regulator - I wondered if it was a case size constraint, but no - a wire ended double AAA holder fits perfectly in the battery compartment, with sufficient space for a bit of foam too.  Amazon reviews say battery life is long, but AAA cells are cheaper and much higher capacity. Wasting the best part of 6V from a low capacity 9V battery is just plain silly.

Hopefully this will be helpful to others looking for longest possible runtime. BTW a small section of plastic cut from a blister pack sandwiches nicely inside the front of the case to protect the otherwise bare LCD.

"Victor Meldrew, the Crimson Avenger!"

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