How are you measuring water and refrigerant line temps?

[stevehull]

Mike,

I have heard of thermal diodes (and their uses), but are these being used in utility/consumer measurement devices?

My understanding was that most all measurement devices (for these uses) are all thermistor or thermocouple. But I would like to know if the thermal diodes are making inroads.

Steve

[AC_Hacker]

I have used:

• thermistors - cheap, simple DIY interface, fairly accurate, good for lower temps
• thermocouple - more expensive, complex DIY interface, more suitable for higher temperatures
• thermal diode - cheap, simple DIY interface, highly accurate, good for lower temps
• 1-wire - cheap (ebay), complex (Arduino) interface, highly accurate, numerical data, good for lower temps

Each of these sensors has their place, an they should all be considered.

But my favorite is the 1-wire/Arduino combination. The learning curve can be a bit steep, but there are examples and libraries that can make it possible. The part I like, even better than the accuracy is that the Arduino is capable of executing additional actions in addition to reading the temperature sensor.

-AC

[jeff5may]

I'm like AC, i like the DS18B20 sensors. They are inexpensive and of acceptable accuracy for my needs. They will plug straight into a huge variety of devices, from inexpensive digital readouts to high-dollar industrial controls. I simply order a dozen or so (ebay total= 20 dollars or less shipped) and test them against each other when they come in. Usually, they read +- 1 degF against each other or less, no need to offset. Just match up the ones that are close to each other and use them in the same device.

For attaching probes directly to pipes/tubes, I use a couple of methods.

For quickie clamp-on devices, plastic potato-chip bag clips work well. I superglue the sensor to one jaw of the clip and a foam earplug to the other. Mount the earplug at a right angle to the sensor so they will self-center. If you're concerned about insulating/contact patch, just slit another earplug and mount the sensor in the slit (like a hot dog in a bun) on one jaw.

For short-term, test-awhile-then-remove type rigs, I use a drop of superglue to secure the sensor, then slather on some toothpaste or sunblock (chap)stick to thermally bond the sensor. Make sure and use something with zinc, titanium, or silicon powder in it. Then wrap with black electrician's tape to form a beehive.

For long term rigs, I use automotive gasket goop and rescue tape. That way, the sensor can be removed and replaced if needed with no special tools or labor. All you need is a knife and some scotch-brite.