Dynisco TX180, Installation And Operation Manual

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TX180 Temperature Transmitter 43
6.3 F
OR
B
EST
M
EASUREMENT
A
CCURACY
The TX180 transmitter is a stable instrument, precision calibrated at the factory for any measurement
range the user may select. However, the automatic cold-junction compensation requires certain
precautions to obtain best accuracy when used with a thermocouple sensor.
The cold-junction compensation operates by attempting to measure accurately the temperature of
the thermocouple terminals on top of the instrument. If these terminals are exposed to thermal
radiation or convection, the cold-junction compensation will introduce an error. With certain types
of thermocouples and temperature measurement ranges, the sensitivity of the cold-junction is
greater than the sensitivity of the measurement couple. Under those conditions, a one degree error
in the cold-junction temperature that the transmitter senses can result in a greater than one degree
temperature measurement error.
For best measurement accuracy with thermocouple sensors, it is advisable to shield the top terminals
by placing the transmitter into a housing or enclosure, such as the model XP-FN, XP-FG, XP-HEAD,
or WP-HEAD. In addition, sufficient time should be allowed for the housing and the transmitter to
reach equilibrium temperature in a given operating environment before best accuracy is reached.
For best accuracy with any sensor, or in the millivolt mode, it is advisable to allow the transmitter to
operate with the desired fixed input signal for a period of 30 seconds before the reading is taken.
The transmitter periodically measures certain internal references. These internal measurements and
the external signal undergo digital averaging and the full accuracy of the instrument is only achieved
after several readings have been averaged.
When using an RTD sensor, a four-wire connection is generally recommended. With a three-wire
RTD the TX180 makes two separate measurements before calculating the temperature, whereas,
only a single measurement is required when using a four-wire RTD. Conceptually, a better accuracy
is possible using a single measurement as compared with calculating the difference of two separate
measurements.
7. A
CCESSORIES AND
I
NFORMATION
Other accessories available from Dynsico are:
LI-1 One-line Local Display
LI-2 Two-line Local Display
XP-HEAD Explosion Proof Housing (No Display Option*)
WP-HEAD Weather Proof Housing (No Display Option*)
XP-FN Explosion / Weather proof Housing with mounting lugs
XP-FG Explosion / Weather proof Housing with mounting lugs and Glass Window
PY-2 Pipe mount bracket to mount XP-FG or XP-FN on 2" pipe
PS-2412 Power Supply, 24/28 VDC, 1.2/0.8A
PS-2405 Power supply, 24 VDC, 0.5A