Model 1140A Design Features
The Ectron Model 1140A incorporates unique features not found in
any thermocouple simulator currently on the market. The combination
of highest accuracy for thermocouple and dc signals, back-lit graphic LCD
display, and many unique functions make the Ectron Model 1140A a very
versatile instrument. This, along with Ectron’s reputation for quality
and performance in thermocouple simulators, will enable the Model 1140A to achieve
wide user acceptance.
The signal output (or input) is available through binding posts
or a mini-thermocouple connector. Cold-junction compensation is controlled
with precision temperature sensors within the terminals to virtually eliminate
errors seen in other thermocouple simulators when used with heavy thermocouple
wire or temperature variations caused by ambient conditions.
Separate offsets for each thermocouple type may be specified from the front
panel. These offsets allow customers to compensate for variations in the
thermocouple or extension wire being used. While these offsets are often greater
than the allowable measurement uncertainty, the Ectron Model 1140A enables users to
compensate for these errors in a known and predictable way that will further
enhance the instrument’s outstanding accuracy.
The accuracy of the Model 1140A is established through the use of ultra-precision
film resistor networks and a precision monolithic voltage reference. The output
is produced with a 24-bit DAC, comprised of discrete and monolithic stages. The
output from each bit of the DAC does not follow a binary sequence. Rather, it
is always less than the sum of outputs of follower bits. In this way, the DAC
output is guaranteed to have no missing output voltages (the inverse of
“no missing codes” in an ADC).
The Model 1140A uses a unique algorithm for its own calibration. The output of
its DAC is measured and the outputs produced from combinations of bits are
compared to the outputs from other combinations to build a matrix of measured
errors. Using this matrix and an overall measurement against an external
standard, the accuracy of each bit is determined and correction factors
stored. In use, these correction factors help determine which bits are
needed to generate the desired output voltage. In this way, the
absolute accuracy of individual components used in the DACs is not nearly
as important as in other instruments, and calibration is virtually a
“hands-off” operation.
Command Features
In addition to the superb accuracy for measure and source modes, this
instrument incorporates many functions under user control. Although
most users will operate the Model 1140A using computer control through one of
the available interfaces, there are several internal functions that allow
many testing and simulation functions to be preset and recalled when needed.
Programmed Functions
The 31 memory locations (files) retain all settable functions of
the instrument: temperature, thermocouple type, reference-junction
temperature, offset, autozero, and lead material (alloy or copper).
In addition, a sequence function is available that allows the user to
sequence through several preset settings (files) with user-specified time
and repeat capability. Thus, a ramp can be programmed either upscale
or downscale or both with preset step size and time.
Autozero Command
One of the Model 1140A’s features is the Autozero command. This
powerful feature allows a user to follow the variation of a signal (either
temperature or voltage) from the point of autozero.
This command, a step in the Output Measure menu, zeroes the readout.
Following this command the readout indicates the
difference between the reading at the time of re-zero and the current
input signal permitting a high degree of resolution.
One of the many applications for the Autozero command is to monitor
the operation of thermostatically controlled temperature chambers.
Setting the zero point of the Model 1140A to the thermostat’s setting,
the Model 1140A will then read the temperature variation allowed by the thermostat
to a high degree of resolution and accuracy.
Offset
This function can correct for a known error in a thermocouple allowing
higher accuracy simulation or measurement. By measuring a
thermocouple’s output at zero or any other temperature using a
precision bath, this error can be programmed into the Model 1140A to
eliminate its effect at that temperature.
See the Model 1140A
product page for more details.
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