Advice for a temperature sensor?

[geb]

 

from their website...

 

"RED Water Temperature

Requires 2 1/16” hole for mounting with back clamp provided. Range is 70-260F. Features ‘Hi” and “Lo” scrolling warning and user adjustable “flashing” warning. Available with high and low memory recall feature. Requires Cyberdyne temperature sender shipped with gauge."

 

 

I'd like to use this gauge for a project but am unable to use the temperature senders that the company provides. I need to make my own. This will be a low temp water cooling circuit.

 

Would one of the LM34 units described at National's site most likely work OK for this?

 

http://www.national.com/mpf/LM/LM34.html

 

Would the plastic LM34DZ TO-92 version be fine or would the 'metal canned'

LM34DH TO-46 be better?

 

Or are there suggestions for a better commonly available sensor component? I've sent a few emails to the cyberdyne company asking for specifications but have got no word as yet.

 

Thanks for any help.

[SH3RL0CK]

I would think you can readily build or buy what you need from a place such as http://www.omega.com, I suggest you take a look here (or similar company) first.

 

Why can you not use the temperature sensors the company provides? I can envision at least two possibilities:

 

1) the sensor element (such as the thermocouple or RTD) doesn't work below 70.

2) The display doesn't work when the signal is indicating a temperature below 70.

 

Of the two, the second seems most likely to me. You should try to find out what type of sensing element they are using. If they are using an RTD, it may be possible to "fool" the device by adding a resistance in series (or parallel) with the sensor. Of course then you would need a correlation table so that when the display is reading 100 degrees you will know the actual temperature is 10 degrees.

[YT2095]

thermistors and thermocouples are NOT directly compatible in ANY way without some support circuitry (an Interface if you like).

 

if you find the LM34 to be compatible, go for the metal case

[geb]

This has been crazy frustrating.

 

When I started out I would have thought that putting a couple of LED readouts on a panel to measure a basic narrow range of temp would be the least troublesome part of this project. Was I wrong. Unbelievable!!!!!!

 

Sure I could have compromised with an LCD readout and just adapted a couple of twenty dollar digital cooking thermometers with probes. This project requires that I read the display from any angle, in bright shop light, at distance. LED was a must. No problem?

 

I searched EVERYWHERE and it just isn't to be done, within reason. This is not for process control but only visual confirmation. And it's not going to the moon on a NASA mission. No cutting edge engineering, no life dependant redundancy. No exotic alloys. I just want a couple of garden variety thermometers here FOR GOD'S SAKE!

 

I finally sprung for a pair of LED automotive variety water temp meters and water pressure meter, all with sending units, from Cyberdyne Gauges. It ain't industrial quality stuff, but pretty much square with my humble needs. The sending units for the temp gauges were way too big to use with my 1/4" copper plumbing, and also too bulky with brass and slow to respond.

 

I dismantled them and discovered that identical part numbers used two different types of thermisor. One SMD and the other a small flat disc. The SMD had an approx 3mm air gap between itself and the body of the sender! You said slow? Dismantled, so much for returning them for replacements. Before all this I thought I'd be into meters and sending units for no more that fifty bucks total. IT'A A THERMOMETER!!!!! It's made in malasia for a cost of three dollars and sixteen cents USD in total parts and labor!!! It's technology that is already decades old. It serves an almost ubiquitous need - measuring fluid temp. HOW HARD CAN THIS BE???

 

No. I'm now into the gauges and senders for about 150.00 USD. About a third of the cost of this total little shop project. Now I have two mismatched thermistors that cannot be measured without an EE degree in hand. My hair is thinning quickly and my wife is onto me about the bottles she discovered behind the basement sofa.

 

I checked out Omega.com thinking I'd just chuck it all and get a fresh start. After forty five minutes on the telephone with a technician THIS IS A GLORIFIED THERMOMETER FOR GOD'S SAKE. I JUST WANT TO MEASURE WATER TEMP!!! I JUST WANT A COUPLE OF GARDEN VARIETY LED PANELS WITH SENDERS TO MEASURE WATER AT TWO POINTS. I'M GOING TO BREAK DOWN AND CRY LIKE A BABY HERE PRETTY SOON. I SWEAR TO GOD!!!

 

...anyway, after forty five minutes of this we've arrived at a bottom line of no less than 450.00 USD. AND I HAVEN'T EVEN DARED TO MENTION A DIMINISHING DESIRE TO MEASURE PRESSURE WITH AN LED AS WELL.

 

Good god. If Kafka had been more interested in tinkering with electronics, he surely could have found rich fodder here at just about any point for a great tale.

[YT2095]

We (SFN) don`t Make the facts, we simply State them.