Solar water heater temp sensors? Buy where?

Anyone know where I can buy water temperature sensors for a solar water heater system?
I want the kind which would screw into the water pipe with say a 1/2
inch fitting. Also called "on-line". And I could use a "T" fitting at the water heater and at the pipe on the roof, then screw these sensors into the "T" fitting (is the idea).
I'm designing/programming my own controller, so just need the sensors.
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If you are designing the circuit there's nothing cheaper than diodes: http://www.micro-examples.com/public/microex-navig/doc/098-temperature-sensor.html
Tape them to the pipe under the insulation. The TO-220 package makes better thermal contact.
Transistor base-emitter junctions work fine too.
jsw
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There are I2C and similar digital output sensors that are quite cheap.
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On Thu, 16 Dec 2010 06:57:22 -0800, "Bill"

Try the auto parts store. They have thermistor based sensors in a good brass screw in package. I use the one with a 1/8" thread (Jeep) in a 1/2" bushing so you have enough meat for threads to mount a spade connector for the common lead. They can be very accurate if you use a whetstone bridge feeding an op amp (LM324) with a pot on the matching leg and a couple 10k resistors for the other legs
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On Fri, 17 Dec 2010 07:33:31 -0800, "Bill"

I use this one on my spa controller The plot I got for the Omix-ADA # 476801 (replaces 3177594) the numbers on the box
750 ohm @ 62f 468 @ 83f 403 @ 90f 342 @ 98f 324 @ 100f
There may be some variation between units but this should get you in the ball park.
I suspect most automotive units are roughly the same. This one said it was for a Jeep and I was using one for a Ford before but the threads were 1/2" requiring a trick to hook up the ground. (I used a ground rod clamp but it was ugly)
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You can make use of the car coolant temperature sensor and connect it to your controller.... no need to redesign the wheel ....
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Can you suggest an appropriate one? Asking the counter clerk to help engineer a project isn't always very productive. Alguien habla Ingls?
jsw
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delphi packard eletric system PART NUMBER 12146312
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Thanks http://www.car-stuff.com/2005buickparkavenuecoolanttemperaturesensor.htm
If I drove up in my 20 year old pickup and asked for a Buick Park Avenue part they might mistake me for a mechanic and give me a discount.
jsw
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