MrHomeScientist
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Thermocouple Advice
I am looking into getting a nice thermocouple to add to my lab equipment, but I know very little about them. The reason I want one is for the
potassium synthesis, in which I will need to measure the sand bath temperature (which will be ~200C). This isn't too demanding, but it would be nice
if I could find one that is chemical resistant so I can use it to directly measure reaction mixes in the future. I did some preliminary searching, and
it looks like K-Type probes go up to about 1300C. That would be neat to have for metallurgy of low melting point metals (Bi, Sn, etc.) as well.
Does anyone have any recommendations for probes that work well in different lab situations? Minimum requirements are that it work for the K synthesis
(measuring a sand bath at ~200C), but it would be nice if it was robust enough to use for other things.
I've seen quite the range of products in a search on eBay, from this cheap one: http://www.ebay.com/itm/251221097301?_trksid=p5197.c0.m619
to this nicer-looking model: http://www.ebay.com/itm/270381494094?ssPageName=STRK:MEWAX:I...
but I'm not sure what to look for in terms of quality.
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Magpie
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I can recommend Omega Engineering - they have a very wide selection. Here's what I use, and like:
http://www.omega.com/ppt/pptsc.asp?ref=KQXL_NQXL
I buy a 12" length, 1/8"diameter, "K" type. I use a PID for readout.
The single most important condition for a successful synthesis is good mixing - Nicodem
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MrHomeScientist
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Thanks Magpie, that does look nice.
That sort of reinforces what I've been seeing when searching for these things - nearly everyone sells the probe, but I never see what it actually
plugs into. Is there a particular device to use with thermocouples, or do different things work? I know you said you use a PID, but I have no
experience with those beyond what google tells me. I have an EE friend that could probably build one, but I imagine we'd still need some data sheet
correlating probe voltage to temperature to get it working.
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watson.fawkes
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Quote: Originally posted by MrHomeScientist  | | That sort of reinforces what I've been seeing when searching for these things - nearly everyone sells the probe, but I never see what it actually
plugs into. Is there a particular device to use with thermocouples, or do different things work? |
What they
plug into, after all is said and done, is a voltmeter that converts the voltage across the thermocouple into a temperature reading. Thus there are
lots of things they plug in to, or are wired into, for fixed applications. You posted two such handheld meters in your original post. I have a
twenty-odd dollar Chinese unit, and it measures temperature just fine. The PID controllers Magpie mentions have screw terminals on the back (as a
rule). You can take off the plug of a thermocouple assembly and screw the lead wires down, or alternately get a thermocouple socket (Omega also sells
them) and install it.
Unless you want something mighty special, I would not recommend trying to roll your own circuit. Too much work. If you want something custom, I'd
recommend osPID, which was built to be modified.
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Magpie
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| Quote: Originally posted by MrHomeScientist | Thanks Magpie, that does look nice.
That sort of reinforces what I've been seeing when searching for these things - nearly everyone sells the probe, but I never see what it actually
plugs into. |
As you can see the mating connector comes with the Omega thermocouple. But you do have to buy some thermocouple wire, probably in some minimum
length. I think I made my hookup to the PID controller with about 10 feet of wire. Give yourself plenty of wire.
The single most important condition for a successful synthesis is good mixing - Nicodem
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MrHomeScientist
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| Quote: Originally posted by watson.fawkes | | What they plug into, after all is said and done, is a voltmeter that converts the voltage across the thermocouple into a temperature reading. Thus
there are lots of things they plug in to, or are wired into, for fixed applications. You posted two such handheld meters in your original post. I have
a twenty-odd dollar Chinese unit, and it measures temperature just fine. |
Well I suppose "never" was too strong a word, since I did find those two! More correct is that it seems to me that the vast majority of sales are for
the probe only. Thanks for the good info, too.
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@Magpie: You're right, the probe you linked doesn't have any wire so it would just stick directly out of the meter, thanks for pointing that out.
I think what I may do is buy the meter in my first eBay link, and also grab the probe you pointed out. As for extension wire: according to the
description on the eBay item it accepts "standard miniature thermocouple connectors." If I'm reading the Omega site correctly, that means I need a
male SMPW-type connector.
They sell ready-made extension cables here, but there is no male SMPW down in the list of connector codes. Do you know if SMP is the same as SMPW? The page was under the mini
connectors heading, so I suspect they are. Option 14 (male SMP to stripped leads) would be the one I want if so.
If you don't know off the top of your head, I can of course just ask the company.
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Magpie
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I don't know about connectors on the meter end of the wire as the PID controller just has screw-down connections. I would call Omega.
The single most important condition for a successful synthesis is good mixing - Nicodem
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metalresearcher
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Type K is rated 1300 C but only for short periods (a few seconds). For continuous use, don't heat it over 1000-1100°C otherwise it will wear quickly.
Consider a Type S (Pt-Pt/Rh) which can be used till 1600°C for a long time.But they are more expensive.
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