ABB TTH300 Operating Instruction page 17

TTH300 HEAD-MOUNT TEMPERATURE TRANSMITTER | OI/TTH300-EN REV. G
Sensor drift monitoring
If two sensors are connected, sensor drift monitoring can be
FDI Package (FIM) enabled via DTM, EDD or
The sensor drift monitoring can be activated for the following
sensor types:
• 2 × resistance thermometer (RTD), two-wire circuit
• 2 × resistance thermometer (RTD), three-wire circuit
• 2 × resistors (potentiometer), two-wire circuit
• 2 × resistors (potentiometer), three-wire circuit
• 2 × thermocouple
• 2 × voltages
• 1 × resistance thermometer (RTD), two-wire circuit, and
1 × thermocouple
• 1 × resistance thermometer (RTD), three-wire circuit, and
1 × thermocouple
• 1 × resistance thermometer (RTD), four-wire circuit, and
1 × thermocouple
To activate sensor drift monitoring, the transmitter must first
be configured for the sensor types referred to above. Following
this, the maximum permissible sensor deviation must be
configured, e.g., 1 K.
Since sensor response times may differ slightly, it is then
necessary to configure a limit time period during which the
sensor deviation has to constantly exceed the maximum set.
If the transmitter registers a larger sensor deviation over the
defined period of time, the diagnostic response configured in
accordance with NE 107 is carried out (tools and LCD display).
Sensor drift monitoring with redundancy operation (devices
with PROFIBUS PA®, FOUNDATION Fieldbus® and HART® to SW-
Rev. 1.03)
If drift monitoring is performed for similar sensors (2 ×
resistance thermometers or 2 × thermocouples), the mean value
from both sensors is mapped on the output signal of the
transmitter as a process variable in redundancy mode.
If a thermocouple is used for drift monitoring of a resistance
thermometer, the resistance thermometer must be connected to
channel 1 and the thermocouple to channel 2 (see Electrical
connections on page 21). The measured value of channel 1
(resistance thermometer) is mapped as a process variable at the
transmitter output.
Sensor drift monitoring with redundancy operation (devices
with HART® from SW-Rev. 3.00)
If a thermocouple is used for drift monitoring of a resistance
thermometer, the resistance thermometer must be connected to
channel 1 and the thermocouple to channel 2 (see Electrical
connections on page 21).
The transmitter output signal always corresponds to the
configured redundancy behavior, see Sensor Redundancy on
page 15.
Note
Before configuring the maximum permissible sensor deviation
with regard to drift monitoring, sensor calibration should be
carried out with reference to the sensor channel 1 value using the
TTH300DTM, for example.
Sensor error adjustment in accordance with Callendar-
Van Dusen
Under normal circumstances, the standard Pt100 characteristic
curve is used for resistance thermometer measurement.
However, recent advances in technology now mean that
maximum measuring accuracy can be achieved where necessary
by carrying out individual sensor error adjustment.
Sensor characteristic curves are optimized by using a Pt100
polynomial in accordance with IST-90 / IEC 751, and EN 60150,
and by applying A ,B, C, or Callendar-Van Dusen coefficients.
With the help of the DTM, EDD or FDI package (FIM), these
sensor coefficients (Callendar-Van Dusen) can be adjusted and
stored in the transmitter as a CVD characteristic curve. Up to
five different CVD characteristic curves can be stored for HART
and PROFIBUS PA, while up to two CVD characteristic curves can
be stored for FOUNDATION Fieldbus.
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