anyone know how to hook up old pyrometer

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I bought an old pyrometer off ebay. its a sim-ply-trol. it can be seen
here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7597923845

It says "iron-constantan" and "ext. res 10 ohm" on the front. So I
guess that means Type J. But what does the ext. res 10 ohm mean?

Also, on the back, there are two screw terminals coming out of the
meter, but one of them has a little plastic dohickey screwed to it
that has some kind of wire wrapped around it which is attached to
another, floating screw terminal, which is shorted to the OTHER panel
mount terminal with a piece of wire. Is this so you can measure meter
temperature without a thermocouple? And do I connect a real
thermocouple directly to the screw terminals, or do I go through the
dohickey?

And how does a mechanical device like this compensate for the cold
junction?

 

[Spehro Pefhany]

I bought an old pyrometer off ebay. its a sim-ply-trol. it can be seen
here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7597923845

It says "iron-constantan" and "ext. res 10 ohm" on the front. So I
guess that means Type J.
Yes.

But what does the ext. res 10 ohm mean?

The thermocouple should be 10 ohms (total loop resistance) for an
accurate reading. The error if you're not at 10 ohms will depend on
the coil resistance (umm.. if you try to measure it, use a digital and
start at a high ohm range so as not to bend the needle accidentally).

Also, on the back, there are two screw terminals coming out of the
meter, but one of them has a little plastic dohickey screwed to it
that has some kind of wire wrapped around it which is attached to
another, floating screw terminal, which is shorted to the OTHER panel
mount terminal with a piece of wire. Is this so you can measure meter
temperature without a thermocouple?

The meter has to measure the temperature at the terminals in order
to read a thermocouple. Also the coil resistance is going to vary with
temperature so there's probably another device inside to help
compensate for that.

And do I connect a real
thermocouple directly to the screw terminals, or do I go through the
dohickey?

I canna see it, but most likely the screw terminals.

And how does a mechanical device like this compensate for the cold
junction?

Something like a bimetal typically. Some don't bother, you just adjust
the 'zero' screw so it reads 70°F or whatever at room temperature and
hope for the best.


Best regards,
Spehro Pefhany

 

[[email protected]]

The thermocouple should be 10 ohms (total loop resistance) for an

accurate reading. The error if you're not at 10 ohms will depend on
the coil resistance (umm.. if you try to measure it, use a digital and
start at a high ohm range so as not to bend the needle accidentally).

I measured the thermocouple resistance, its 6.4 ohms (DMM across
thermocouple leads).

I measured the meters resistance (DMM across direct screw terminals)
25 ohms

How do I figure out what the error should be?

Thanks,

Asa

 

[Spehro Pefhany]

I measured the thermocouple resistance, its 6.4 ohms (DMM across
thermocouple leads).

I measured the meters resistance (DMM across direct screw terminals)
25 ohms

How do I figure out what the error should be?

Thanks,

Asa

Put a few ohms metal film in series with the T/C (keep the leads
short-- bend them into a 'U') and don't worry about it. Those things
are VERY crude at the best of times.



Best regards,
Spehro Pefhany

 

[whit3rd]

I bought an old pyrometer off ebay. its a sim-ply-trol. it can be seen
here:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7597923845

It says "iron-constantan" and "ext. res 10 ohm" on the front. So I
guess that means Type J. But what does the ext. res 10 ohm mean?

Typically, it indicates that calibration will meet specs if the
external
resistance of the thermocouple wire is 10 ohms or less.

And how does a mechanical device like this compensate for the cold
junction?

It's intended for hot furnaces (type J is good for 1600F) so ten
degrees
one way or the other is not important. Probably no cold junction
compensation.

 

[[email protected]]

Typically, it indicates that calibration will meet specs if the
external
resistance of the thermocouple wire is 10 ohms or less.

10 ohms or less? Not exactly 10 ohms? So if my thermocouple measures
6.4 ohms I am good to go? Also, this meter goes from 0 to 300C, does
that mean its probably meant to be more accurate than a 1600F one?

 

[Spehro Pefhany]

10 ohms or less? Not exactly 10 ohms?

Exactly 10 ohms. Modern electronic indicators have a maximum
resistance (usually at least 100 ohms).

So if my thermocouple measures
6.4 ohms I am good to go? Also, this meter goes from 0 to 300C, does
that mean its probably meant to be more accurate than a 1600F one?

Maybe.


Best regards,
Spehro Pefhany

 

[Rich Grise]

10 ohms or less? Not exactly 10 ohms? So if my thermocouple measures
6.4 ohms I am good to go? Also, this meter goes from 0 to 300C, does
that mean its probably meant to be more accurate than a 1600F one?

Try it! Connect it the way that looks obvious, and get a thing of
ice water and a thing of boiling water and see what readings you get.

Good Luck!
Rich

 

[[email protected]]

Try it! Connect it the way that looks obvious, and get a thing of
ice water and a thing of boiling water and see what readings you get.

Good Luck!
Rich- Hide quoted text -

- Show quoted text -

I did. It seems to work okay for ice water, but boiling water went way
beyond 125C on the meter. I measured the water with another known good
K type thermocouple and digital meter and it was 99C.

I guess this meter is F-ed. But what goes bad in a mechanical meter
like this? Its all metal right? Looks like I wasted $50

 

[Rich Grise]

I did. It seems to work okay for ice water, but boiling water went way
beyond 125C on the meter. I measured the water with another known good
K type thermocouple and digital meter and it was 99C.

I guess this meter is F-ed. But what goes bad in a mechanical meter
like this? Its all metal right? Looks like I wasted $50

I wouldn't say it's fried - it deflects, right? But the different reading
might be what the little unknown thingie on the back is - a calibration
thing or something.

It's worth further investigation.

Cheers!
Rich

 

[Spehro Pefhany]

I did. It seems to work okay for ice water, but boiling water went way
beyond 125C on the meter. I measured the water with another known good
K type thermocouple and digital meter and it was 99C.

I guess this meter is F-ed. But what goes bad in a mechanical meter
like this? Its all metal right? Looks like I wasted $50

- maybe it's connected wrong and that thing has to be in series

- I'd expect an error of only about +11% with the resistance the
way you have it (about 10'C on 80'C above room temperature) if
the correct total resistance is 35 ohms.



Best regards,
Spehro Pefhany

 

[Jasen]

I did. It seems to work okay for ice water, but boiling water went way
beyond 125C on the meter. I measured the water with another known good
K type thermocouple and digital meter and it was 99C.

I guess this meter is F-ed. But what goes bad in a mechanical meter
like this? Its all metal right? Looks like I wasted $50

maybe it needs all of the 10 ohms resistance (and you currently have 6?)
try adding some resistance in series with the cold thermocouple.

Bye.
Jasen