DMM thermocouple

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Moby

www.mobytransformers.com BV.8, Bv.11, Bv.12, T14/1
GDIY Supporter
Joined
Jun 3, 2004
Messages
2,122
Location
Serbia
Hi guys.
I have few of DMM's but just one, cheapo (http://uni-trend.com/productsdetail.aspx?ProductsID=631&ProductsCateId=748&CateId=748) has temperature measuring option. From the manual I see that is capable to measure up to 1000c but the package probe goes up to 260 (or300c). My question is: what kind of probe I can buy to measure temperatures above? I don't expect 1% accuracy but +/-10c will do the job.
Can I go with K type thermocouple like this?
https://www.ebay.com/itm/K-Type-Thermocouple-Probe-High-Temperature-Sensors-with-M8-Threads-3m-Lead-/171913269407
 
> Can I go with K type thermocouple

With 5-buck thermocouples you don't really need a "temperature measuring option" DMM.

You need two Type K, a glass of ice, and a chart like this:
https://www.thermocoupleinfo.com/type-k-thermocouple.htm

Wire the thermocouples in series. Both at the same temperature, they should add to zero. Put one (reference) in ice water (zero degrees C). Put the other where you want. Read the mV. Look in the chart.

25mV is 602 degrees +/-7 degrees, +/- DVM error.

What the "special" DMM gives you is an in-built "reference junction and ice", and conversion from mV to Deg *for a specific thermocouple type* (which apparently does not go to 1,000C).
 
Hey PRR, thanks for giving me  the reason to finally buy ice machine ;)
Btw, I will use this approach to test the "special meter". After I "calibrate" the system with the precision milivoltmeter I can attach the sensors  to  this "special beast" :)
 
Looking back:

25mV is 600 deg C. The typical low-cost DMM will hardly resolve 1mV, plus 1-count display bobble, is possible 2mV error. 2mV on 25mV is 50 deg error, more than you asked for.

You need micro-Volt resolution. This used to be expensive. I know the DMMs are getting much better. If that is not available, every time the chip-makers improved DC accuracy they published a plan for a thermocouple amp to boost sub-mV signal up so a common meter would read it. Today uV accurate chips are inexpensive (though maybe not sold in all shops). A common TL072 is 4mV error but with trimming you might get it near 0.1mV for many minutes at a time.
 
Hey, I tried with probes in series, cant read the damned thing. I went with one and cheapo DMM  at temperature  settings and it works. Im not sure how accurate it is, but I read some reasonable values. I will check with the boilig water ;)
 

Latest posts

Back
Top