VTI Instruments Ametek EX1200A Series, User Manual

Page: 98 / 165

www.vtiinstruments.com
EX1200A Triggering 97
Digits
The resolution, or number of digits, can be set for temperature measurements. Either 3½, 4½, 5½,
or 6½ digits can be selected. Resolution should be optimized based on application and required
results. While lower resolution yields faster sampling rates, it also decreases the accuracy of the
reading. Unlike other functions, the digits of a temperature measurement do not directly correlate
to the number of significant digits for a given measurement, but follow the values listed in
Table 4-11.
Transducer Type 6.5 digits 5.5 digits 4.5 digits 3.5 digits
Type B TC 0.01 °C 0.1 °C 1 °C 10 °C
Type E TC
0.001 °C 0.01 °C 0.1 °C 1 °C
Type J TC 0.001 °C 0.01 °C 0.1 °C 1 °C
Type K TC 0.001 °C 0.01 °C 0.1 °C 1 °C
Type N TC 0.001 °C 0.01 °C 0.1 °C 1 °C
Type R TC
0.01 °C 0.1 °C 1 °C 10 °C
Type S TC 0.01 °C 0.1 °C 1 °C 10 °C
Type T TC 0.001 °C 0.01 °C 0.1 °C 1 °C
RTD 0.01 °C 0.1 °C 1 °C 10 °C
Thermistor 0.01 °C 0.1 °C 1 °C 10 °C
T
ABLE
4-11: T
EMPERATURE
R
ESOLUTION
Built-in Sensor Support
To simplify temperature measurement configuration, several sensor have been predefined in the
SFP and in the driver APIs. See Table 4-10 for a list of predefined sensors. All constants and
conversion parameters needed for these sensors are built into the DMM allowing them to be
directly configured and used.
Custom/User-Defined Sensors
Although several sensors are predefined for temperature measurements, the EX1200A DMM also
offers the ability to define custom sensors to add flexibility to a test system. For thermocouples,
custom types are defined at the application level by using the measured voltage value and passing
it to a software-defined look-up table. For custom RTDs or thermistors, the parameters defined in
Table 4-10 must be defined as appropriate.
Using a Thermocouple
To perform a temperature measurement using thermocouples, a reference junction temperature
must be used to calculate the hot junction temperature. The reference junction temperature can be
obtained using a known,
fixed junction temperature, an external thermistor or RTD measurement,
or by using the onboard, internal thermistor of an EX1200A series terminal block (on supported
terminal blocks only).
When a fixed reference temperature is used, it must be provided as a value -20°°C and +80°°C
(again, all temperature measurements must be made in °C).
For measurements using an external or fixed reference, a reference temperature must be stored
from a previous RTD or thermistor reading. To do so, set a multiplexer card channel up for an
RTD/thermistor measurement and then set this measurement as the external reference. When a
measurement is initiated on this channel, it will be handled as an external reference and the
temperature will be stored in the volatile memory of the reference register. Any thermocouple
measurements made after the reference temperature has been defined will use this value. The
external reference value will be used until another external reference measurement is made or until
the mainframe is powered off.
Fixed temperature references typically provide the best accuracy, provided the fixed temperature
is maintained at a constant temperature. Although the internal isothermal block references of the