Hi
Some nameless cretin decided it would be a good idea to streamline
the selection of signal cable connectors on a current little device
I'm playing with.

We have K type two pin connectors for everything carrying digital or
analogue signals, apart from thermocouples of course because this is a
"quality job" using PT100,s, none of your cheapo thermocouples here!

Of course the fact that the K type connector cannot accomodate the
compensating cable is a different matter entirely :-)

There are a gross of possible problems, which will all become obvious
on first use, but my main concern is the fact that these connectors
are in a damp environment and the chrome/ nickel- Aluminium/ nickel
pins connected to copper wire will I'm sure corrode to a state that
will produce problems in weeks or months.

Has anyone come across an instance of copper cable being used with
these connectors?

I would guess that ist isn't a frequent configuration as I am still
waiting for a reply from the supplier.

AB

On Sat, 02 Sep 2017 08:42:58 +0100, Chris Hogg wrote:

On Sat, 02 Sep 2017 03:47:01 +0100, Archibald Tarquin Blenkinsopp
wrote:

Hi
Some nameless cretin decided it would be a good idea to streamline
the selection of signal cable connectors on a current little device
I'm playing with.

We have K type two pin connectors for everything carrying digital or
analogue signals, apart from thermocouples of course because this is a
"quality job" using PT100,s, none of your cheapo thermocouples here!

Of course the fact that the K type connector cannot accomodate the
compensating cable is a different matter entirely :-)

There are a gross of possible problems, which will all become obvious
on first use, but my main concern is the fact that these connectors
are in a damp environment and the chrome/ nickel- Aluminium/ nickel
pins connected to copper wire will I'm sure corrode to a state that
will produce problems in weeks or months.

Has anyone come across an instance of copper cable being used with
these connectors?

I would guess that ist isn't a frequent configuration as I am still
waiting for a reply from the supplier.

AB

Is your application so critical that it requires precise temperature
measurement, in turn requiring that the t/cs be connected via
compensating cable rather than simple copper cable? I don't know
exactly what difference it makes, but I doubt it's more than a few
degrees, BIMBW. To be really precise, you should have a
temperature-controlled cold junction in the circuit (not a lot of
people know that).


V-------------------------------EMF-------------------------V


-----------------\ /------------------\ /------------
metal A \ / metal B \ / metal A
\ / \ /
V V
hot cold
junction junction

My experience was with studio pottery kilns using Type R thermocouples
(Pt/Pt-13%Rh), and I did connect them with the appropriate
compensating cable (orange sheath; yours should be green if IEC or BS,
see
http://tmseurope.co.uk/applications/...es-tolerances),
but I always thought it was a bit overkill for my application. The
connectors come in different sizes IIRC, so you can size them to the
cable. But t/c cables don't carry significant current so don't have to
be very large.

My set-up was in a garden shed, unheated, and potentially damp in
winter. I wasn't aware of any corrosion problems with the connectors.
Perhaps wrap them in insulating or self-amalgamating tape to keep out
the damp if it's of concern in your application.

Thanks, tape isn't an option this is a "quality job" :-)

There is not a single thermocouple used anywhwere to measure anything,
so cold junctions do not matter unless there is an influence on the
PT100 bridge current. This will become obvious though on first use.

I too have used copper wire to connect TC's, and not had a problem,
the cold junction was always in the instrument providing the
measurement incidentally. I would not used copper for a serious long
term measurement strategy though, hence my lack of experience with
this type of setup.

I do recollect having problems with damp connections on more
conventional connectors in a similar application that seemed to be
exacerbated by the use of aluminium bootlace ferrules, so the
reactivity is the item of concern. Anything else can be quantified and
rectified.


AB

I too have used copper wire to connect TC's, and not had a problem,
the cold junction was always in the instrument providing the
measurement incidentally. I would not used copper for a serious long
term measurement strategy though, hence my lack of experience with
this type of setup.

I do recollect having problems with damp connections on more
conventional connectors in a similar application that seemed to be
exacerbated by the use of aluminium bootlace ferrules, so the
reactivity is the item of concern. Anything else can be quantified and
rectified.


AB

Back when Ford built a brand new factory near Valencia for the new
Fiesta, I went out there to commission the paintshop bake ovens. The
electrical contractor had no idea about the importance of the correct
use of Thermocouple compensating cable, and the long runs were
connected randomly. The effect of this was that some zone burners were
running flat out, while others were idling, and there was a total lack
of control of oven temperature. Once this was sorted out, it worked
properly. Until then, it was chaos.

--
Davey.

Davey submitted this idea :
Back when Ford built a brand new factory near Valencia for the new
Fiesta, I went out there to commission the paintshop bake ovens. The
electrical contractor had no idea about the importance of the correct
use of Thermocouple compensating cable, and the long runs were
connected randomly. The effect of this was that some zone burners were
running flat out, while others were idling, and there was a total lack
of control of oven temperature. Once this was sorted out, it worked
properly. Until then, it was chaos.

It must be an Italian thing...

When I was out there, a French guy whom I got friendly with, who was
staying in our hotel in Brescia, had exactly the same problems
commissioning a process oven, except they had been wired in copper.

On Sat, 02 Sep 2017 12:39:26 +0100, Harry Bloomfield
wrote:

Davey submitted this idea :
Back when Ford built a brand new factory near Valencia for the new
Fiesta, I went out there to commission the paintshop bake ovens. The
electrical contractor had no idea about the importance of the correct
use of Thermocouple compensating cable,

It must be an Italian thing...
Even though Valencia is in Spain?

When I was out there, a French guy whom I got friendly with, who was
staying in our hotel in Brescia, had exactly the same problems
commissioning a process oven, except they had been wired in copper.

G.Harman

on 02/09/2017, supposed :
Even though Valencia is in Spain?

:/

On Sat, 2 Sep 2017 11:49:52 +0100, Davey
wrote:


I too have used copper wire to connect TC's, and not had a problem,
the cold junction was always in the instrument providing the
measurement incidentally. I would not used copper for a serious long
term measurement strategy though, hence my lack of experience with
this type of setup.

I do recollect having problems with damp connections on more
conventional connectors in a similar application that seemed to be
exacerbated by the use of aluminium bootlace ferrules, so the
reactivity is the item of concern. Anything else can be quantified and
rectified.


AB

Back when Ford built a brand new factory near Valencia for the new
Fiesta, I went out there to commission the paintshop bake ovens. The
electrical contractor had no idea about the importance of the correct
use of Thermocouple compensating cable, and the long runs were
connected randomly. The effect of this was that some zone burners were
running flat out, while others were idling, and there was a total lack
of control of oven temperature. Once this was sorted out, it worked
properly. Until then, it was chaos.

Not quite the same approach as no actual thermocouples are in use
anywhere in the system.

There may be problems with the PT100 signals though, any other
analogues would be swamped by the 4mA min.

As I said, I am expecting anomolies and thanks to digital displays
these will be all too obvious.

The only think I cannot factor in is the possibility of corrosion,
this will take weeks to appear, as I mentioned I have no experience of
terminating K type connectors with copper wire.

Regards

AB

On Sat, 02 Sep 2017 18:31:34 +0100, Chris Hogg wrote:

On Sat, 02 Sep 2017 17:37:54 +0100, Archibald Tarquin Blenkinsopp
wrote:

The only think I cannot factor in is the possibility of corrosion,
this will take weeks to appear, as I mentioned I have no experience of
terminating K type connectors with copper wire.

Regards

AB

Just a thought, but are you sure that the actual connectors (blades
and terminals) are made of the same materials as K-type thermocouples?
I ask, because this site doesn't specify which type of thermocouple to
use them with:
http://www.tc.co.uk/thermocouple/the...connectors.htm

It might be worth abrading one or both of the blades with a bit of
sandpaper to see if they're actually just copper.

And if you scroll down, you'll see larger sized connectors for heavier
cable.

Following the k type further

"Manufactured in accordance with standard EN 50212
?High purity thermocouple alloys used for male pin and female socket
constructions
??Bevel tipped pins for easy insertion
Polarised flat pins
Related Connectors"


Some indeed have obviously different colours, but K do look like a
standard nickel plated connector




AB

On Sat, 02 Sep 2017 19:46:45 +0100, Chris Hogg wrote:

On Sat, 02 Sep 2017 19:11:02 +0100, Archibald Tarquin Blenkinsopp
wrote:
Following the k type further

"Manufactured in accordance with standard EN 50212
?High purity thermocouple alloys used for male pin and female socket
constructions
??Bevel tipped pins for easy insertion
Polarised flat pins
Related Connectors"


Some indeed have obviously different colours, but K do look like a
standard nickel plated connector




AB

RS do an uncompensated version with copper terminals. They're
colour-coded white. http://tinyurl.com/y8v2s73w

Thanks!

You solved a long standing conundrum that bothered me a little from
time to time.

The RS 4-20mA current injector uses just such a connector.

I did wonder why on earth a company would produce a test instrument
with a connector normally associated with tc,s.

Methinks I know why we went down the route of a thermocouple plug/
socket also.

The genius ordering the connectors would have had access to one of the
RS calibrators.

He probably thought green was a nicer colour though.

It will be a nice job replacing a hundred or so when they do give
problems :-(

AB

Chris Hogg wrote:
Is your application so critical that it requires precise temperature
measurement, in turn requiring that the t/cs be connected via
compensating cable rather than simple copper cable? I don't know
exactly what difference it makes, but I doubt it's more than a few
degrees, BIMBW. To be really precise, you should have a
temperature-controlled cold junction in the circuit (not a lot of
people know that).

I thought by definition you got a cold junction, whether you wanted one or
not? The trick being that you should put the cold junction compensation (ie
the thermistor, or chip with a semiconductor temperature sensor) close to
the cold junction (where you solder/crimp/whatever to the hot junction
leads) so that it is at the same temperature as the inherent cold junction.
The cold junction doesn't have to be in an ice bucket, just there be minimal
difference between the cold junction and the sensor which is used to
compensate.

The problem with a non-compensated cable is the cold junction then becomes a
long way from the compensating sensor and so there can be temperature
differential between the two. Particularly problematic if there are large
heating appliances involved.

Theo