Datasheet

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A GREATER MEASURE OF CONFIDENCE
Temperature Measurements — Calibration
SWITCH/MEASURE SYSTEMS
16
Integra Series Multimeter/Switch Systems
Cold Junction Compensation Methods
Thermocouple measurements always require that the temperature be known at the point where the
thermocouple is connected to the instrument. This connection point is known as the “cold junction.”
The Integra systems support three different methods for including this “cold-junction” temperature in the
temperature measurements.
Automatic CJC
The CJC sensors are mounted on the multiplexer module’s PC board (7700, 7706, 7708, and 7710).
They sense the actual temperature across the module’s connector, then compensate all temperature
measurements accordingly. The CJC scaling is done automatically when autozero is turned on, so the
user does not have to acquire it separately. When autozero is turned off, the instrument is optimized
for speed and does not refresh the CJC compensation. This allows the user to obtain faster scan rates
for short periods of time while ambient temperature remains stable.
External CJC
A thermistor or RTD is attached to Channel 1 by the end user. This thermistor or RTD is then used to
measure the temperature of the point(s) where the thermocouples are connected to the instrument
or to copper wires leading to the instrument. The precision of the actual temperature measurement
depends on the accuracy of the cold junction reading and how close the sensor is to the actual tem-
perature of the connection.
Simulated CJC
When the “change” in temperature is of interest rather than the absolute temperature value, the user
can enter a parameter as a cold junction reference point (for example, 23°C for room temperature).
This parameter will be used to adjust the actual temperature measurement for each channel. This sim-
ulated temperature must be updated manually if ambient conditions change. This is also the method
used when an actual ice bath is used to establish a cold junction of 0°C. The simulated parameter is
then set to 0°C or 32°F.
Open Thermocouple Detect
A system can alert the user if any thermocouple becomes broken or otherwise disconnected from the
input terminal blocks. When the Open T/C Detect feature is enabled, the system will perform (in the
background) a two-wire resistance measurement across each thermocouple input channel. If an open
connection is detected, the front panel display will show “OVERFLOW” for that channel.
Calibration
The design of the Integra Series and their calibration procedure were developed to address a variety of
critical calibration issues. For example, the systems have front panel input jacks, so there’s no need to dis-
assemble the system for periodic recalibrations. There’s also no need to buy, stock, and track spare “cal
only” modules. The systems are connected to the calibrator through the front panel input jacks. The sys-
tems’ calibration procedure covers both verification and adjustment and can be performed through either
the front panel or any of the remote interfaces. The calibration interval is user-selectable.