RP,

Yes, the wire I am using is the correct type (type T for type T
thermocouples). The only other temperature gradient at a "connection
point is in the back room where it can be significantly colder than
where the thermocouple is located. For instant in one room it could be 0
C while in the backroom it could be -25 C. I was told by the
manufacturer of the wire and thermocouple (Omega Engineering) that this
should not pose a problem. I tend to disagree. The extensions wire is
terminated in an isothermal block (from National Instruments,
cfp-tc-120). Originally, I thought that the extreme cold could be
radianting through the wire and affected the connector block directly. I
am still unsure whether this is the case and if so how to fix the
problem.

 

I guess another thing to check is that there is no temperature

gradient at the various cable joins - (T/C to extension cable,

extension cable to equipment). These connections should be made at an

"isothermal block" and wrapped in thermal insulation to prevent any

temperature difference between the two wire joins.

 

And you are using the correct type of extension cable for the

thermocouples in use of course?

 

RP

 

On 16/01/2008, Spehro Pefhany <speff@interlog.com> wrote:

> Quoting "Chaoua, Rashid" <rashid.chaoua@lmco.com>:

> 

> > Hi,

> >

> > I have problem reading accurate temperatures using thermocouples. I
have

> > a 40' long refrigerator divided into 4 compartments (3 rooms used
for

> > testing and the fourth houses my electronics). In each room I have a

> > thermocouple suspended from the ceiling to mid-height of the room.
These

> > thermocouples are connected via thermocouple extension wire to a

> > National Instruments cFP-1804 module and connected to an isothermal

> > connector block. Additionally, each room is kept at different

> > temperatures (ie- room 1: -10C, room 2: -15C, room 3: -20C, room 4:

> > -30C) and the wire is terminated in the coldest room (room 4).

> >

> >

> >

> > My problem is as rooms 1-3 are heated up (via heaters) the
temperatures

> > read are incorrect. If I read the temperatures at the thermocouple

> > directly they read the correct room temperature. When I read the

> > temperature at the end of the thermocouple extension wire it reads a

> > much colder temperature (I am using a handheld meter). The same
problem

> > occurs when I use my National Instrument device. I need the
temperatures

> > read to be accurate (I have a program that uses these temperatures
to

> > make a series of decisions) but am unable to find out why I am
having

> > such problems. Can anyone out there lend there expertise?

> >

> > Rachid

Rachid 

 

 

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