Ordering
information: (Model) - (Thermocouple Type) - (Pre-Calibrated
Temperature Range)
- Select IRt/c(*) model. Example:
IRt/c.3X
- Select the thermocouple type
(**) desired (J, K, etc.), add it to the model name.
Example: IRt/c.3X-K
- Select the target temperature
range. For example, to control a lamination process
at 200 F (93 C), look at the following target temperature
table for 200 F (93 C). Note the black area in the
table indicates the "180F/90C" pre-calibrated
range. Add this to complete your selection.
Example: IRt/c.3X - K - 180F/90C.
Additional note: The above table
indicates the temperature ranges where the IRt/c’s match
standard thermo-couple signals.
This allows for highly accurate measurement and control
in the ranges selected. IRt/c’s require no power
supply and can be connected directly to thermocouple
inputs of controllers, PLC’s, transmitters, and other
t/c devices.
In addition, all IRt/c sensors
are useable over the entire specified target temperature
range for each sensor. Signal output
tables and polynomials are available from Exergen.
Accuracy
IRt/c’s are pre-calibrated at
the factory for typical target material emissive properties,
but actual emissivi-ties may
differ. The accuracies specified assume that the precalibrated
value is correct for your installation, or
that the single point set up of Tech Note #1 has been
performed to reduce the error to zero at the calibra-tion
point (which is normally the set
point for a temperature control system).
1. Using Non-Programmable
Thermocouple Interface Devices
Standard non-programmable thermocouple
input devices deliver a high level of accuracy and repeatability
with IRt/c’s for most temperature
measurement and control of factory automation, process
control and OEM machinery.
For example, if an IRt/c is calibrated to measure and
control a non-metal target at 200°F (90°C)
set point, the error will be ±0% or ±0.02°F (0.01°C)
at the set point. As the target temperature varies
from the
original set point temperature,
the error increases slightly according to the Accuracy
Table (below). For example,
if the interface device is set for 0% error at 200°F
(90°C), then at the extremes of the temperature
range of 190°F to 210°F (87°C to 99°C), the error would
be ±0.4% or 1°F (0.6°C). This gradual error
is caused by a difference in linearity between the output
of the IRt/c compared to standard thermo-couples.
For detailed explanation, consult
Tech Note #89.
2. Using
Programmable Thermocouple Interface Devices, OEM, PLC,
Computers
With programmable controllers,
microprocessors, PLC, or computer interface, the error
can be reduced to a small
value even over a very wide temperature range. As shown
in the Accuracy Table, IRt/c’s produce high
accuracies over a wide temperature range when the application
requires it. For programming, contact Exergen
for output signal tables.
Accuracy
Table
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*Percent is of reading. For wide
target temperature variations, target emissivity variations
may cause greater errors. Multipoint calibration
is recommended
in such cases, and can reduce errors to less than 0.1%.
3. Repeatability Error is
< 0.01°C (0.02°F)
Repeatability error, defined
as the ability of the IRt/c to reproduce a reading under
the identical conditions, is
extraordinarily small. There are no active electronics
to shift, and no source of spurious signals until the
limit of resolution is reached,
which is 0.0001°C, due to Johnson noise.
4. Interchangeability Error
is ± 1% or0.5 °C (1 °F)
Interchangeability error, defined
as the difference in reading between any two IRt/c’s
of the same model making
identical measurements, is of particular importance
to users of multiple IRt/c’s such as OEM’s, or
when an IRt/c must be replaced. The unit-to-unit consistency
of IRt/c’s permits the same calibration settings
to be used for all subsequent installations for the
same target material and temperatures. Inter-changeability
specification applies only to
the signal generated by the IRt/c in its precalibrated
range.
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