Design And Function; Input Functionality; Sensor Redundancy; Sensor Drift Monitoring - ABB TTH300 Series Operating Instruction

TTH300 HEAD-MOUNT TEMPERATURE TRANSMITTER | OI/TTH300-EN REV. E

4 Design and function

Digital transmitters are communication-ready devices with
microprocessor-controlled electronics. They conform to the
requirements of IP rating IP 20 and are suited for integration
into DIN A and DIN B sensor heads.
With HART® transmitters, an FSK signal is superimposed on the
4 to 20 mA output signal in accordance with the HART standard
to facilitate bidirectional communication.
With PROFIBUS PA® transmitters, communication takes place in
accordance with PROFIBUS-MBP (IEC 61158-2), PROFIBUS PA
Profile 3.01.
With FOUNDATION Fieldbus® transmitters, communication
takes place in accordance with the FOUNDATION Fieldbus H1
(IEC 61158-2), ITK Version 5.x.
The transmitters can be configured, polled, and tested using a
DTM or an EDD.
As an option, the transmitter can be fitted with a type A or a type
AS LCD indicator. Type AS is used exclusively for visualizing
current process values. Type A also supports the option of
configuring the transmitter. It is recommended that you use this
combination.
The electrical connection between the LCD display and
transmitter is provided by a 6-pin flat ribbon cable with a plug
connector. The LCD display can only be operated when
connected to transmitters that have an LCD display interface.

Input functionality

Sensor Redundancy

To enhance system availability, the TTH300 has two sensor
inputs.
The second sensor input can be used redundantly for both
resistance thermometers (2 x three-wire circuit or 2 x two-wire
circuit) and thermocouples, or for a mixture of the two.
Sensor redundancy (or sensor backup) always involves
measuring the temperature of the two sensors and calculating
the mean value on the basis of this.
This value is provided at the output of the transmitter. Should a
sensor fail, the temperature measurement for the sensor that
remains in operation is provided at the output of the
transmitter.
A relevant diagnosis notice is available via DTM, EDD,
FDI Package (FIM) or on the LCD indicator. The measured value
remains available and maintenance measures can be taken at the
same time.

Sensor drift monitoring

When two sensors are connected, sensor drift monitoring can be
activated via the DTM, EDD or FDI Package (FIM).
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 records a larger sensor deviation during the
defined time period, a 'Maintenance required' diagnosis
information is generated through HART, EDD and DTM in
accordance with NE 107. At the same time, diagnostic
information is shown on the LCD indicator.
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