Note
A scan list must include a reference temperature channel before related
thermocouple channels, or the fixed reference temperature must have been
supplied before starting to scan thermocouple channels (see following section).
Thermocouple
Reference Temperature
The isothermal reference temperature is required for thermocouple
temperature EU conversions. The Reference Temperature Register must be
loaded with the current reference temperature before thermocouple channels
are scanned. The Reference Temperature Register can be loaded two ways:
1. By measuring the temperature of an isothermal reference junction
during a scan.
2. By supplying a constant temperature value (that of a controlled
temperature reference junction) before a scan is started.
Setting-up a Reference
Temperature Measurement
The
[SENSe:]REFerence <
sensor_type
>,<
sub_type
>,[<
range
>,](@<
ch_list
>)
command links channels to the reference temperature EU conversion.
When the channel is scanned, the reference temperature is measured and
stored in the Reference Temperature Register, the FIFO, and the CVT. The
reference value is applied to all subsequent thermocouple channel
measurements until another reference temperature value is stored in the
Reference Temperature Register.
•
The
<
ch_list
>
parameter specifies any sense channel that is
connected to the reference temperature sensor.
•
The
<
sensor_type
>
parameter can specify
THERmistor
,
RTD
, or
CUSTom
. This is a resistance temperature measurement and uses the
on-board 122
µ
A current source for all types.
•
The
<
sub_type
>
parameter must specify:
–
For RTDs;
85
or
92
(for 100 Ohm RTDs with 0.003
85
or 0.003
92
Ohms/Ohm/Degree C temperature coefficients, respectively).
–
For Thermistors; only
5000
(See previous note on page 75).
–
For CUSTom; only 1 (contact your HP Field Engineer for Custom
EU algorithms).
•
The optional
<
range
>
parameter can be used to choose a fixed A/D
range. When not specified or set to
AUTO
, the module uses autorange.
To set channel 12 to measure the isothermal reference temperature on the
HP E1413’s terminal module (with built-in 5,000 Ohm thermistor) send
SENS:REF THER,5000,(@112)
On-board thermistor connected
to channel 12.
Chapter 3
Using the HP E1313/E1413 77
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