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Amplifiers
Thermocouple Input Amp (AR-GXTCK/J)
When two different types of metal are connected to make
a circuit and there is a temperature difference between
both ends of the joined part, an electric current flows. A
thermocouple uses this phenomenon. You can connect a
K type thermocouple (CA: Chromel Alumel) to the AR-
GXTCK, and a J type thermocouple (IC: Iron
Constantan) to the AR-GXTCJ. A K type thermocouple
generates a large electromotive force, and you can mea-
sure to a comparatively high temperature (up to 1200˚C
with the AR-GXTCK). A J type thermocouple generates
a similarly large electromotive force, and you can mea-
sure to a comparatively low temperature. With the GX-1,
the lower temperature range of both is down to –50˚C.
Both the AR-GXTCK and the AR-GXTCJ use special
dedicated connectors (GIM-K1 and GIM-J1), and you
connect a thermocouple by matching the plus and minus
connectors. In the K type, Chromel is plus; in the J type,
Iron is plus.
Calibration is not necessary. In each range, however, the
rated value (in AD values: –25000) on the minus side is
–50˚C. So to obtain the temperature ˚C you do not just
multiply the SLOPE value by the AD value; you also add
the Y_OFFSET value.
For example, if you use the AR-GXTCK to measure in a
range of 1200˚C, the AD value is made to –21950. To
covert this to a temperature, multiply by the SLOPE
value 0.025, and add the Y_OFFSET value of 575. This
calculation obtains a temperature of 26.25˚C.
The SLOPE value 0.025 is determined as follows:
The rated values (for an AD value: ±25000) are each
+1200 and –50, so:
(
− −
1200
50
(
− −
25000
25000
The Y_OFFSET becomes a temperature of 575˚C when
the AD value is 0.
4-26
)
=
0 025
.
)
Filters
Analog Filter
The analog filter is a 2nd order Butterworth low-pass fil-
ter (–12 dB/oct). The cutoff frequency can be selected
independently of the sampling frequency. To prevent
aliasing, the cutoff frequency must be set to 50% or less
of the sampling frequency.
Digital Filter
The digital filter using a DSP can attenuate from 40% of
the set sampling frequency. The digital filter is not func-
tional at sampling frequencies of 200 kHz, 100 kHz, and
50 kHz.
Calibration
Zero and gain self-calibration using a DSP is performed
whenever power is turned on, and whenever the input
range or the sampling frequency is changed. The signal
used for calibration is built into the amp.
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