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Author Topic: REQ: temperature sensor can measure -100 °C  (Read 1272 times)
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smainj
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« on: July 21, 2009, 12:02:43 00:02 »

Hi
pls i need temperature sensor  can measure -100°C  and how i can read with ADC converter
thank you for your help
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Parmin
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« Reply #1 on: July 21, 2009, 02:28:35 02:28 »

WOW.. thinking of building a cryogenic tank?
Preserving some bodies mayhaps?
Or experiment in super conducting?

Would love to hear more about this..
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bbarney
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« Reply #2 on: July 21, 2009, 04:28:00 04:28 »

Fiber optic temp sensor
http://www.engineershandbook.com/Components/temperaturesensors.htm
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smainj
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« Reply #3 on: July 21, 2009, 10:27:03 10:27 »

@Parmin the cryogenic tank  is build and work fine
i have to read the temperature and save the data in PC every 15 min
@ bbarney
i found sensor only for hot temperature
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cipiloi
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« Reply #4 on: July 21, 2009, 10:35:12 10:35 »

Hi ! Hier -200 to +800   http://www.picotech.com/pt100_sensors.html
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bbarney
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« Reply #5 on: July 21, 2009, 04:18:53 16:18 »

another option
http://www.minco.com/products/sensors.aspx?id=38
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anaKu
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« Reply #6 on: July 21, 2009, 10:22:46 22:22 »

It depends on the accuracy and the cost target. If you can touch or penetrate the object you measure, then I would recommend either Platinum resistance device like the PT100 series (very high accuracy but a bit expensive), or type T thermocouple (good accuracy, cheap).

The PT100 sensor can be bought in different shapes to probe or attach to the medium you measure, and it works by having a very precise resistance vs. temperature dependency. You need to build a bridge where the PT100 is one of its legs, and feed the output to an instrumentation amplifier (or good opamp if you don't have much electrical noise in the area).

The thermocouple is just a pair of dissimilar metals (copper / constantan) that you either buy as a probe with a connector or bare wires, or as a spool of wire. If you buy a spool, you need to weld the two wires together at one end - this is the measurement end, and also weld the other end together and put it at known temperature. There is an electrical voltage developed by having one junction hotter than the other, and you measure the voltage (in the 10-100's of microvolts range) with good instrumentation/opamp circuit. In lab environment, people put the reference junction in an ice bath for a good known temperature, but in industrial measurements, the reference junction is just at the ambient and being compensated by a thermistor.
I used both systems in the past, and it is fairly easy to build.
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smainj
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« Reply #7 on: July 22, 2009, 12:34:53 00:34 »

i think  www.minco.com have good sensor and easy to use than the thermocouple
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bbarney
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« Reply #8 on: July 22, 2009, 01:13:09 01:13 »

i think  www.minco.com have good sensor and easy to use than the thermocouple

Thats what I thought too when I found it ,couldn't tell you prices so you will need to contact them for more info
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anaKu
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« Reply #9 on: July 23, 2009, 12:27:28 00:27 »

As I said, the most common contact temp sensors are either based on thermocouples (and for -100 C type T is a good one) or on PT100 (platinum resistance sensor) which is very accurate.
Most of the sensors at www.minco.com are based on these two types, packaged as ready-to-use sensors configuration (note : RTD , Resistance Temperature Detectors, is actually PT100).
There are hundreds of companies that sell packaged sensor tips, insertion rods, washers and all kind of configurations, but the sensor itself inside the package, and this will lead you to the choice of electronics, is most probably either thermocouple or PT100.

If you just want to buy a packaged sensor, you may also want to try www.omega.com - I used them in the past and they have quite a variety. They also have good engineering docs on their site.
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« Reply #10 on: July 23, 2009, 12:30:33 00:30 »

 anaKu
What kinda of price tag do these sensors usally run, I don't need them but just curious as to the cost
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anaKu
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« Reply #11 on: July 23, 2009, 03:35:53 03:35 »

T/C wires run about $1/ft (you need a small resistance welder to weld the tips of the 2-wire cable to make a measurement junction). Ready-made probe prices depend on configuration size, sheath material, insulation etc. Washer T/C (the simplest) runs about $10-$15 each. 4" probes in SS304 sheath and bare wire termination are about $30 each. T/C connectors are about $4 each.
PT100 are much more expensive - double and triple the cost - but they are more accurate and the electronics is simpler.
www.omega.com provides prices on-line for various probes and wires - you configure what you want and see the price generated immediately. They are good for small quantity purchases, but for larger quantities you can do much better price-wise at other places.
« Last Edit: July 23, 2009, 03:39:30 03:39 by anaKu » Logged
bbarney
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« Reply #12 on: July 23, 2009, 01:31:20 13:31 »

I didn't think it would be that cheap,very reasonable pricing considering the conditions some of these probes will be in
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