Data Translation DT9871, User Manual

Page: 94 / 134

Chapter 6
94
Out of Range Data for RTD Channels
Each RTD type corresponds to an allowable voltage range. If a voltage is measured on the
input that is outside of the legal range for the selected RTD type, the channel may be
configured for the wrong type of RTD or something other than an RTD may be connected to
the channel.
For channels configured with a RTD type of voltage, the Limit (LMT) LED on the rear panel of
the instrument lights to alert you when the voltage is out of range (greater than +1.25 V or less
than –1.25 V); see
page 37 for the location of this LED. For channels configured with an RTD
type other than voltage, the LMT LED lights when the temperature limit is out of range for the
specified RTD type.
In addition, if the input voltage is less than the legal voltage range for the selected RTD type,
the software returns the value TEMP_OUT_OF_RANGE_LOW (–88888.0 decimal). If the
input voltage is greater than the legal voltage range for the selected RTD type, the software
returns the value TEMP_OUT_OF_RANGE_HIGH (88888.0 decimal).
Out of Range Data for Voltage Channels
Each voltage input channel has an allowable voltage range (±10 V or ±60 V on MEASURpoint
instruments). You configure the input range for each channel using software. If a voltage is
measured on the input that is outside of the legal range for that channel, the Limit (LMT) LED
on the rear panel of the instrument lights to alert you; see
page 37 for the location of this LED.
Resolution
TEMPpoint, VOLTpoint, and MEASURpoint instruments support a resolution of 24 bits for
the analog input subsystem; you cannot specify the resolution in software.
Calibration
Each TEMPpoint, VOLTpoint, and MEASURpoint instrument is factory-calibrated to meet or
exceed its published specifications using standards traceable to NIST.
The calibration process includes multiple steps. First, the A/D on each channel is calibrated
for offset and gain; these values (including the zero point) are stored in ROM. Then, each CJC
circuit is calibrated for thermocouple input channels, and the reference current is
characterized for RTD channels.
While each instrument was designed to preserve high accuracy measurements over time, it is
recommended that your instrument be recalibrated every year to ensure that it meets or
exceeds specifications.
You can calibrate your instrument in the field using precise calibration equipment and the
Measurement Calibration Utility, described on
page 15 .