24 TTF300 FIELD-MOUNT TEMPERATURE TRANSMITTER | OI/TTF300-EN REV. I
… 4 Design and function
… Input functionality
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 will be carried out (tools and LCD
indicator).
Sensor drift monitoring with redundancy operation (devices
with PROFIBUS PA®, FOUNDATION Fieldbus®, and HART® to
SW-Rev.: 01.03)
If drift monitoring is used for the same sensor types
(2 × resistance thermometer or 2 × thermocouple), the average
value calculated from the two sensors will be mapped to the
transmitter output signal as a process variable in redundancy
mode.
If a thermocouple is used for resistance thermometer drift
monitoring, the resistance thermometer should be connected to
Channel 1 and the thermocouple to Channel 2 (see Electrical
connections on page 29). 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.: 03.00)
If a thermocouple is used for resistance thermometer drift
monitoring, the resistance thermometer should be connected to
Channel 1 and the thermocouple to Channel 2 (see Electrical
connections on page 29).
The transmitter output signal always corresponds to the
configured redundancy behavior, see Sensor redundancy on
page 22.
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
TTF300 device drivers (FDIX/DTM/EDD), 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.
The device drivers (FDIX/DTM/EDD) can be used to set and store
these sensor coefficients (Callendar-Van Dusen) 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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