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First experience with IR thermometer

J

John - KD5YI

Jan 1, 1970
0
I was prompted by a discussion in another thread on this forum to buy one of
those contactless IR thermometer guns. It is an IR4890 by IWH.

I tried to measure the temperature of a surface mount resistor. The
thermometer shows about 25 to 26C but the resistor is hot enough to cause me
to immediately remove my finger from it.

The thermometer works on some other objects but has trouble with the PCB
solder mask and surface mount resistors. Can anybody explain this?

Thanks,
John
 
I

Ian Stirling

Jan 1, 1970
0
John - KD5YI said:
I was prompted by a discussion in another thread on this forum to buy one of
those contactless IR thermometer guns. It is an IR4890 by IWH.

I tried to measure the temperature of a surface mount resistor. The
thermometer shows about 25 to 26C but the resistor is hot enough to cause me
to immediately remove my finger from it.

Look at the beam size.
A laser indicator does NOT mean that the sensing size is the same size.
it'll typically be several degrees.
It will not read typical surface mount resistors accurately - they are too
small.
 
J

John - KD5YI

Jan 1, 1970
0
Ian said:
Look at the beam size.
A laser indicator does NOT mean that the sensing size is the same size.
it'll typically be several degrees.
It will not read typical surface mount resistors accurately - they are too
small.

The laser has a center dot and then 12 dots around the central dot forming a
circle. They say it samples the area of the circle. I put the gun so close
to the resistor that all the dots merged into one (as far as I could tell).
Also, the resistor is a size 2010.

Thanks,
John
 
J

John Larkin

Jan 1, 1970
0
The laser has a center dot and then 12 dots around the central dot forming a
circle. They say it samples the area of the circle. I put the gun so close
to the resistor that all the dots merged into one (as far as I could tell).
Also, the resistor is a size 2010.

Thanks,
John

Three issues:

If the surface emmisivity of the target is low, the thermometer will
read low. The resistor end caps will almost certainly be shiny, low e,
and the middle might be low, too.

A surfmount resistor will usually be hotter in the middle than on the
ends.

The laser indication of the effective sampling area probably isn't
accurate very close up. Your manual may address this in the fine
print.

John
 
S

scada

Jan 1, 1970
0
John Larkin said:
Three issues:

If the surface emmisivity of the target is low, the thermometer will
read low. The resistor end caps will almost certainly be shiny, low e,
and the middle might be low, too.

A surfmount resistor will usually be hotter in the middle than on the
ends.

The laser indication of the effective sampling area probably isn't
accurate very close up. Your manual may address this in the fine
print.

John

Some guns will give correction factors for a given emmisivity. Usually there
is a correction table for aluminum, steel, plastics, etc... I have
successfully used it to check temps of mosfets, transistors, with TO220
cases.
 
C

Chuck Olson

Jan 1, 1970
0
John - KD5YI said:
The laser has a center dot and then 12 dots around the central dot forming a
circle. They say it samples the area of the circle. I put the gun so close
to the resistor that all the dots merged into one (as far as I could tell).
Also, the resistor is a size 2010.

Thanks,
John

Most IR gun type thermometers with laser beam projectors do not use a beam
splitter for both IR and Laser to be on the same axis. You may have to move
the laser pattern a specific amount of offset to get the resistor in the IR
sensor's field of view for very close work. My Raytek Raynger ST appears to
have an offset of about 13mm.

Chuck
 
J

John - KD5YI

Jan 1, 1970
0
John said:
Three issues:

If the surface emmisivity of the target is low, the thermometer will
read low. The resistor end caps will almost certainly be shiny, low e,
and the middle might be low, too.

A surfmount resistor will usually be hotter in the middle than on the
ends.

The laser indication of the effective sampling area probably isn't
accurate very close up. Your manual may address this in the fine
print.

John


The manual doesn't address much of anything. It appears that you are right,
though, about the laser and accuracy up close. That was quite a revelation
to me.

Still can't get the resistor to read much over room temp. The PCB, however,
is saying up to 94C in spots. Another revelation.

Thanks for your input.

John
 
J

John - KD5YI

Jan 1, 1970
0
Chuck said:
one of


cause me



Most IR gun type thermometers with laser beam projectors do not use a beam
splitter for both IR and Laser to be on the same axis. You may have to move
the laser pattern a specific amount of offset to get the resistor in the IR
sensor's field of view for very close work. My Raytek Raynger ST appears to
have an offset of about 13mm.

Chuck


You are correct. Thanks for pointing that out.

I still can't seem to get the resistor to show much above ambient, however.

Thanks,
John
 
J

John - KD5YI

Jan 1, 1970
0
Chuck said:
one of


cause me



Most IR gun type thermometers with laser beam projectors do not use a beam
splitter for both IR and Laser to be on the same axis. You may have to move
the laser pattern a specific amount of offset to get the resistor in the IR
sensor's field of view for very close work. My Raytek Raynger ST appears to
have an offset of about 13mm.

Chuck

Aha! I had not been paying attention to the gun's IR input area. By
carefully placing the gun such that the resistor is on the sensing hole
axis, it seems to be working.

Call it pilot error.

Thanks to all for pointing this out.

John
 
R

Rene Tschaggelar

Jan 1, 1970
0
John said:
I was prompted by a discussion in another thread on this forum to buy
one of those contactless IR thermometer guns. It is an IR4890 by IWH.

I tried to measure the temperature of a surface mount resistor. The
thermometer shows about 25 to 26C but the resistor is hot enough to
cause me to immediately remove my finger from it.

The thermometer works on some other objects but has trouble with the PCB
solder mask and surface mount resistors. Can anybody explain this?

The thermopile does not make a peak measurement.
It integrates the radiation from the beam angle,
however wide this beam is. You only get a good
reading from a target that covers the whole angle
and is equal in temperature over this area.

Rene
 
R

Robert Baer

Jan 1, 1970
0
Rene said:
The thermopile does not make a peak measurement.
It integrates the radiation from the beam angle,
however wide this beam is. You only get a good
reading from a target that covers the whole angle
and is equal in temperature over this area.

Rene
Furthermore it ASSuMEs a fixed radiation coefficent (field
emissitivity of 0.98), which is patently false when sweeping from a
rough colored surface to a reflective (solder) surface.
 
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