Ectron 1140A - Precision Voltage Source (Alloy Output); Precision Voltmeter (Alloy Input); Thermocouple Offset

Theory of Operation
simulated reference junction set in the THERMOCOUPLE → REF JCT TEMP menu, T
AZ
is the
autozero offset temperature (if autozero is enabled), and T
OFFSET
is the offset temperature set in
the THERMOCOUPLE → THERMOCOUPLE OFFSET menu.
Precision Voltage Source (Alloy Output)
The general equation for the Model 1140A when it is used as a precision voltage source in the
alloy mode is
V
OUTPUT
= V
SOURCE
− f
cn
(T
REFJCN
) + f
cn
(T
OFFSET
),
where V
OUTPUT
is the voltage produced at the output terminals, V
SOURCE
is the user-specified voltage
shown on the display, T
REFJCN
is the temperature of the simulated reference junction set in the
THERMOCOUPLE → REF JCT TEMP menu, and T
OFFSET
is the offset temperature set in the
THERMOCOUPLE → THERMOCOUPLE OFFSET menu.
Precision Voltmeter (Alloy Input)
The general equation for the Model 1140A when it is used as a precision voltmeter in alloy mode
is
V
METER
= V
INPUT
+ f
cn
(T
REFJCN
) − f
cn
(T
OFFSET
) − V
AZ
,
where V
METER
is the measured voltage shown on the display, V
INPUT
is the input voltage applied at
the terminals, T
REFJCN
is the temperature of the simulated reference junction set in the
THERMOCOUPLE → REF JCT TEMP menu, T
OFFSET
is the offset temperature set in the
THERMOCOUPLE → THERMOCOUPLE OFFSET menu, and V
AZ
is the autozero offset voltage (if
autozero is enabled).
Thermocouple Offset
The thermocouple offset, accessible through the THERMOCOUPLE → THERMOCOUPLE OFFSET
menu, is intended to be an offset at the temperature of the Model 1140A terminals, and is not an
offset at the simulated (or measured) temperature.
The offset applied is computed using the Seebeck coefficient for the current thermocouple type,
at the temperature of the front-panel terminals in use. As such it can be used to compensate for
an error of a thermocouple calibrated at the environment of the Model 1140A, and is not
intended to compensate for thermocouple errors at other temperatures.
Note that the sense of the offset value can be thought of as a correction to the actual
thermocouple emf. Thus, if the calibrated thermocouple’s output was less than the standard emf
for that type, the correction applied would need to be positive. On the Model 1140A, a positive
value would be entered in the THERMOCOUPLE OFFSET menu.
7-3