Measuring water temp with K type thermocouple?

[SNGLinks]

I wish to measure how my hot water temperature changes with time. I have a Uni-T UT71B that comes with a K type thermocouple.

Can I put the thermocouple directly in the water or will the water's conductivity upset the result?

[Richard Crowley]

Thermocouples are extraordinarily LOW impedance. They are two pieces of wire welded together.
It seems unlikely that leakage from that near-zero impedance circuit over to ground would have any significant effect on the measurement.

Fresh water is generally high-impedance (high-resistance) at DC. Water with impurities (such as sea-water) has much more resistance, but still many orders of magnitude higher than a thermocouple circuit which is near-zero.

The real question, IMHO, is how do you insert the thermocouple into the water stream?  And what exactly is this water you are measuring?  I wouldn't stick just any old thermocouple of unknown origin into drinking/cooking water. And maybe not into bathing/shower/laundry water either, at least until you thoroughly clean it, etc. There are special enclosed versions of thermocouples designed for use in potable water.

Of course, if you are simply thrusting the thermocouple into a running stream out of the tap momentarily, there probably is no sanitation issue.

[SNGLinks]

Thanks for your reply.

I have a fault with my hot water system (a combi boiler) The water intermittently runs cold whilst taking a shower.
I would like a graph of temp against time to show the 'engineer' who comes to try to repair it again.

[Richard Crowley]

You could clamp the thermocouple onto the side of an exposed pipe (or tap, or showerhead, etc.)

[SNGLinks]

 

You could clamp the thermocouple onto the side of an exposed pipe (or tap, or showerhead, etc.)

I could do that but it would be a bit laggy because of the thermal inertia of the pipe.
I want to show that the water suddenly goes cold.

[Seekonk]

Sounds like a classic case of calcium buildup in the pipe core of the heater.  If an external tank, the cold water source internal dip tube could be broken at the top.  That prevents feeding cold water to the bottom of the tank.  Instead it feeds into the top diluting the hot water quickly.

[Richard Crowley]

Yeah, if you want good "transient response" then you will need to hang the thermocouple joint right inside the stream of water.