Exergen D-Series IR Scanner
Compare the Exergen Microscanner D-series thermometer with conventional
alternatives:
Common Surface
Temperature
Measurement Factors |
Microscanner
D-series IR
Thermometers |
Conventional IR "Point and Shoot" guns and probes, including
laser
aimed units |
Conventional
contact probes, thermocouples,
RTD's,
thermistors |
1. Pre-set Emissivity errors? |
no effect |
very sensitive |
no effect |
2. Emissivity shift errors? |
no effect |
very sensitive |
no effect |
3. User adjustment errors? |
no effect |
very sensitive |
no effect |
4. Background reflection errors? |
no effect |
very sensitive |
no effect |
5. Contact errors? |
no effect |
no effect |
very sensitive |
6. Friction heating errors? |
no effect |
no effect |
very sensitive |
7. Heat sinking errors? |
no effect |
no effect |
very sensitive |
8. Time based errors? |
no effect |
no effect |
very sensitive |
The D-Series is an
entirely different type of instrument than conventional temperature
measuring devices. Designed specifically for the highest possible
accuracy, it is the only infrared instrument which can be certified as
to NIST-tracable accuracy on real surfaces of unknown emissivity, while
completely free of contact errors and heat sinking errors of contact
devices.
1. Pre-set
Emissivity errors
The true emissivity of a surface is known only
approximately. Conventional IR devices without Exergen's Automatic
Emissivity Compensation System can only display an approximate
temperature over their entire temperature range. The "accuracy"
specifications given by most manufacturers are only for a "black body"
calibration and do not hold outside laboratory conditions. Black body
calibrations do not include emissivity shifts, ambient change effects on
the target, and other phenomena that introduce significant errors.
2. Emissivity
shift errors
Even if an IR "gun" is set to the correct emissivity to read a surface
accurately at a particular temperature, it does not mean that the IR
"gun" will read the same target correctly at other temperatures.
Emissivity of virtually all surfaces changes with temperature. A common
assumption for conventional IR thermometry is that emissivity is
constant with changes in target surface temperature. Real materials do
not have this characteristic.
3. User Adjustment
Errors
A setting of
emissivity = 0.9 on an IR "gun" from one manufacturer will not
necessarily match that of another IR "gun" manufacturer. There are no
standards set in the industry on the precise measurement and meaning of
"emissivity".
Also, Quality Assurance programs should not rely upon any instrument
that allows users to alter the instrument settings and to let it display
whatever the user wishes.
4. Background
Reflection Errors
Even if emissivity is constant (see #2), there are still errors induced
by changing ambient temperatures. For example, with emissivity = 0.9,
ambient reflections account for 10% of the signal that the IR "gun" will
see. If ambient changes, the IR "gun" will display a different target
temperature, even if the target remains at the same temperature.
5. Contact Errors
Thermocouples, RTDs. thermistors, and other contact devices only
measure their own temperature. They do not measure surface
temperature. Published "Accuracy" specifications are for the probes
only, not the surfaces they must measure. Users must guarantee that the
probes are brought the same temperature as the surface. Can you
guarantee that your probes are brought to the same temperature as the
targets to be measured?
6. Friction heating errors
For moving surfaces, a contact probe is prone to frictional heating. The
size of the error is dependent on the roughness of the surface, the
speed, the coating on the probe, and so on. It is impossible to control
all the variables.
7. Heat sinking errors
For most non-metals, heat sinking errors can be quite large. The heat
transfer rate of the metal leads required on "contact probes" conducts
heat faster than the target material can replace, resulting in unknown
and fairly large errors. In general, the less dense the target material,
the larger the heat sinking error with a contact probe.
8. Time based errors
Contact temperature probes are slow. The temperature of a target can
change more quickly than most probes, resulting in errors in real time
measurement. |