dataTaker DT80, User Manual

Page: 316 / 417

UM-0085-B09 DT80 Range User Manual Page 316
RG
Channel Types
The DT80 supports all commonly-recognized thermocouple types:
Type Positive Negative Range
B
Pt, 30%Rh Pt, 6%Rh +50 – +1820 °C
C
W, 5%Re W, 26% Re 0 – +2320 °C
D
W, 3%Re W, 25%Re 0 – +2320 °C
E
Ni, 10%Cr Cu, 45%Ni -270 – +1000 °C
G
W W, 26% Re 0 – +2320 °C
J
Fe Cu, 45% Ni -210 – +1200 °C
K
Ni, 10%Cr Ni,2%Mn, 2%Al -270 – +1372 °C
N
Ni, 14%Cr, 1%Si Ni, 4%Si, 0.1%Mg -270 – +1300 °C
R
Pt, 13%Rh Pt -50 – +1768 °C
S
Pt, 10%Rh Pt -50 – +1768 °C
T
Cu Cu, 45%Ni -270 – +400 °C
Each type has characteristics (sensitivity, stability, temperature range, robustness and cost) that make it appropriate for
particular applications.
The DT80's thermocouple linearisation data are based on the ITS90 International Temperature Scale.
Channel Options
The applicable channel options for thermocouples are as follows
•
GL
x
,
ES
n
, as for voltage measurements
• the channel factor specifies a scaling factor, as for voltage channels
If an external isothermal block is used then the
TR
(temperature reference) and/or
TZ
(electrical zero reference) options
should be specified for the channels used to measure reference junction temperature and reference junction electrical
zero. See
Isothermal Block Support (P316)
below.
Using Thermocouples with the DT80
Thermocouples are wired to the DT80 as for any other voltage input,
see Voltage (P303)
. Be sure to connect the
thermocouple the right way around – for K type thermocouples the red wire is normally negative and would therefore be
wired to the # or – terminal.
The channel type is a
T
t
where
t
is the thermocouple type. So to measure a K-type thermocouple you would use the
TK
channel type, e.g.
4TK
for a thermocouple wired to channel 4's + and – terminals, or
4-TK
if the thermocouple is wired
between – and #.
Using the thermocouple channel type reads the channel as a voltage and automatically applies reference junction
compensation and linearization.
By default, the DT80 uses an internal temperature sensor to measure the reference junction temperature. You can check
the reading of this sensor using the
REFT
channel type.
Each CEM20 channel expansion module includes its own temperature sensor, which is used for any thermocouple
measurements made using that CEM20. This sensor can be read using the
n
REFT
channel type, where
n
is the CEM
number (1-15).
Isothermal Block Support
For higher accuracy measurements, the DT80 also supports the use of an external isothermal block . In this case the
isothermal block's temperature sensor is measured by a separate DT80 channel. This channel uses the
TR
channel
option to identify it as the temperature reference – its reading will then be used as the reference for all subsequent
thermocouple measurements in that schedule.
For example:
RA10S 5AD590(TR) 1..4TT
In this example four T-type thermocouples are measured. Their reference junctions are enclosed in an isothermal block,
along with an AD590 temperature sensor, which is connected to analog channel 5.
If the isothermal block is already compensated (i.e. it is held at 0°C) then it is not necessary to measure its temperature.
Instead, use
11SV(TR)
as reference channel (system variable
11SV
always returns 0.0).
To further enhance accuracy, you can use another DT80 channel to measure the electrical "zero" at the isothermal block
in order to compensate for any voltage offsets between the logger and the reference junctions. This is done by running a
separate pair of wires (similar to those used for the thermocouple channels) from the DT80 to the isothermal block, at
which point they are shorted together.