DESCRIPTION
The Ectron T/CMate Model 200 Thermocouple Cold-Junction Compensator
allows any following instrumentation amplifier to be used as
a thermocouple amplifier with thermocouple input. Ectron conditioner-amplifiers
are ideal.
The T/CMate accepts thermocouple signals, provides
precision cold-junction compensation to copper wires, and
adapts the signal for amplification. A jumper allows selection of the
appropriate compensation for four thermocouple types.
A unique optical isolator provides power for the compensation circuitry
from any 5 V dc to 15 V dc power source, eliminating
the need for batteries. The strain-gage excitation supply
available from Ectron conditioner-amplifiers provides ideal
power. When connecting to computer I/O cards, the computer’s 5 V
or 12 V supply voltages can be used.
OPERATION
When thermocouple signals are amplified or converted to digital
signals the T/C wires must first be connected to copper wires
(amplifiers using T/C wires haven’t yet been invented).
Where the T/C to copper wires connect, unwanted T/C junctions
are formed. To avoid these errors a “Cold Junction Compensator” (CJC)
must be used.
Historically, CJC devices have taken several forms:
An ice bath (slurry of pure water and ice).
A thermoelectrically cooled chamber.
A battery-powered bridge network that includes
temperature correction.
The Ectron T/CMate is similar to Type
3, but instead of a battery almost any nonisolated power
supply from 5 V to 15 V can be used.
Within the T/CMate isolation between the low-level
T/C signals and the power supply voltage is extremely high.
Any number of T/CMates can be powered by a single power supply.
The T/CMate does not linearize the signal. Linearization to match
thermocouple conversion characteristics is most accurately
accomplished by a computer following a linear analog
amplification of the actual thermocouple output.
 ENLARGE
IMAGE
SPECIFICATIONS
Thermocouple types: E, J, K, and T selectable
by use of plug jumper.
Input Thermocouple Connection: Two
thermocouple wires plus shield attach to a terminal block
assembly.
Dc Power: 5 V dc to
15 V dc regulated at 50 mA nominal, usually supplied by the
amplifier’s excitation supply but can be any supply.
Isolation Between Signal and Input Power:
100 MΩ and 75 pF. Breakdown voltage ±300 V.
Accuracy (including ambient variation of
25°C ±25°C):
Better than ±1°C for all thermocouple types.
Reference
Temperature: 0°C (32°F)
Zero/Operate Switch: A toggle
switch shorts the compensated T/C output to simplify zero
adjustment of the following amplifier.
Size: 30 mm H x 30 mm
W x 51 mm L (1.15” H x 1.15” W
x 2.005” L) plus 165 mm (6.5”) cable.
Weight: 65 g (2.3 oz) plus connector if installed.
Output: Standard
output for the Model 200 is a 165 mm (6.5”)
cable with wires for the compensated T/C output signal
plus two leads for input power. It has
soldered ends for terminal block or other connection.
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