thermocouple relay is their such???? - PLCS.net

mer · June 13th, 2010, 01:55 PM

Hello again i've started another project and i have limited inputs and i need to read several kilns with one reader so my question is,,is their a relay made that can or could read thermocouple (j or K )wire through the relay or if anyone knows some sort of way to read several points with one reader im game to any idea thanks in advance..Mer..

Ron Beaufort · June 13th, 2010, 02:10 PM

something along these lines? ...

http://www.omega.com/Temperature/pdf/OSW_SW14.pdf

Phill77 · June 13th, 2010, 02:10 PM

I have been trying to find some locking thermocouple plugs, still had no luck with that.

However, one supplier I spoke to told me to use any connector I wanted to, as so long as there is no temperature differential across the connector it won't act as a cold junction and affect the measurement significantly in my application.

Whether this is true for all temperature ranges I don't know, but I would be tempted to set up a trial using any old relay you like to see if it does actually affect the measurement.

Mickey · June 13th, 2010, 02:15 PM

More links

http://www.omega.com/toc_asp/subsect...perature&all=1

http://www.newportus.com/products/acccalib/thmowire.htm

mer · June 13th, 2010, 02:33 PM

Quote:

Originally Posted by ron beaufort

something along these lines? ...

http://www.omega.com/temperature/pdf/osw_sw14.pdf

thanks dat be it !!!

mer · June 13th, 2010, 02:35 PM

Quote:

Originally Posted by phill77

i have been trying to find some locking thermocouple plugs, still had no luck with that.

However, one supplier i spoke to told me to use any connector i wanted to, as so long as there is no temperature differential across the connector it won't act as a cold junction and affect the measurement significantly in my application.

Whether this is true for all temperature ranges i don't know, but i would be tempted to set up a trial using any old relay you like to see if it does actually affect the measurement.

i have connected thermocouple wire with a butt connector and has threw the reading off by 40deg...

danw · June 13th, 2010, 04:05 PM

Quote:

Originally Posted by mer

i have connected thermocouple wire with a butt connector and has threw the reading off by 40deg...

What the supplier said is true. If there is no temperature difference between the connection points, there will be no error. Getting connection points to be isothermal (no temperature difference between them) can be problematic.

The scheme is functionally a de-multiplexor, many inputs to one output. There has to be no temperature difference between (+) & (-) terminals at both input and output.

You are practically guaranteed a temporary error if you are handling the connectors and the wire while crimping a connector terminal, you finish, and connect it. Your body heat has transferred to the wire/connector.

Drafts or circulating air in a panel can heat/cool some terminals and not others. Any temperature difference between the connection terminals is a direct error at the cold end of the thermocouple. Shielding the connection points from any draft of air, whether cooling or convection heat is a wise idea.

The polarity of the thermocouple wires has to match.
+ has to switch to +
- has to switch to -
You can be big errors by swapping polarity.

The type thermocouple wire has to be identical on both input and output. K to K, J to J, etc.

keithkyll · June 14th, 2010, 04:47 PM

Get connectors at Omega too. Two styles, both need a good crimper tool.
MTC
D'Sub

briancr · June 15th, 2010, 01:47 AM

We use a similar situation here, multiple temp. probes into one analogue input. OEM used a multiplexer card, and this works very well in our situation

June 13th, 2010, 01:55 PM	#1
mer Member Join Date: Dec 2009 Location: Asheville nc Posts: 54	thermocouple relay is their such???? Hello again i've started another project and i have limited inputs and i need to read several kilns with one reader so my question is,,is their a relay made that can or could read thermocouple (j or K )wire through the relay or if anyone knows some sort of way to read several points with one reader im game to any idea thanks in advance..Mer..

June 13th, 2010, 02:10 PM	#2
Ron Beaufort Lifetime Supporting Member Join Date: Jul 2002 Location: Charleston, SC Posts: 4,227	something along these lines? ... http://www.omega.com/Temperature/pdf/OSW_SW14.pdf __________________ 2-B ? Best regards, ----+----] [----+------------( )---- Ron \| \| PLC Training Boot Camp \| 2-B \| +----]/[----+ I once was lost, but now am found, was blind, but now I see.

June 13th, 2010, 02:15 PM	#4
Mickey Lifetime Supporting Member Join Date: May 2003 Location: Palmdale,Ca Posts: 7,523	More links http://www.omega.com/toc_asp/subsect...perature&all=1 http://www.newportus.com/products/acccalib/thmowire.htm __________________ Mickey If you want happiness for an hour-take a nap. If you want happiness for a day-go fishing. If you want happiness for a month-getmarried. If you want happiness for a year-inherit a fortune. If you want happiness for a lifetime-help someone else. ----- Chinese Proverb

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June 13th, 2010, 02:10 PM	#3
Phill77 Member Join Date: Aug 2005 Location: Northants Posts: 29	I have been trying to find some locking thermocouple plugs, still had no luck with that. However, one supplier I spoke to told me to use any connector I wanted to, as so long as there is no temperature differential across the connector it won't act as a cold junction and affect the measurement significantly in my application. Whether this is true for all temperature ranges I don't know, but I would be tempted to set up a trial using any old relay you like to see if it does actually affect the measurement.

June 14th, 2010, 04:47 PM	#8
keithkyll Member Join Date: Jul 2005 Location: Lucas, TX Posts: 1,150	Get connectors at Omega too. Two styles, both need a good crimper tool. MTC D'Sub

June 15th, 2010, 01:47 AM	#9
briancr Member Join Date: Jul 2007 Location: Pietermaritzburg Posts: 175	We use a similar situation here, multiple temp. probes into one analogue input. OEM used a multiplexer card, and this works very well in our situation

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