SMAR TT301 - Disassembly Procedures for Transmitter

Maintenance Procedures
5.3
Symptom: CURRENT OF 21.0 mA OR 3.6 mA
Probable Source of Trouble:
 Transmitter Connection
 Check if the sensor is correctly connected to the TT301 terminal block.
 Check if the sensor signal is reaching the TT301 terminal block by measuring it with a multimeter at
the transmitter-end. For mV and thermocouples test can be done with connected and disconnected
to the transmitter.
 Sensor
 Check the sensor operation; it shall be within its characteristics.
 Check sensor type; it shall be the type and standard that the TT301 has been configured to.
 Check if process is within the range of the sensor and the TT301.
NOTE
A 21.0 or 3.6mA current in XMTR mode indicates burnout.
Symptom: INCORRECT OUTPUT
Probable Source of Trouble:
 Transmitter Connections
 Check power supply voltage. The voltage at the TT301 terminals must be between 12 and 45V, and
ripple less than 0.4V.
 Check for intermittent short circuits, open circuits and grounding problems.
 Noise, Oscillation
 Adjust damping
 Check grounding of the transmitters housing, extra important for mV and thermocouple input.
 Check the terminal block for moisture.
 Check that the shielding of the wires between sensor/transmitter and transmitter/panel is grounded
only in one end.
 Sensor
 Check the sensor operation; it shall be within its characteristics.
 Check sensor type; it shall be the type and standard that the TT301 has been configured to.
 Electronic Circuit Failure
 Check the integrity of circuit replacing it with a spare one.
 Calibration
 Check calibration of transmitter.
Disassembly Procedure
Refer to Figure 5.1. Make sure to disconnect power supply before disassembling the transmitter.
Sensor
If the sensor is mounted on the transmitter, first disconnect the wires in order to prevent the wires from
breaking. To access the terminal block, first loose the cover locking screw on the side marked "Field
Terminals", then unscrew the cover.
Electronic Circuits
The main board (6) and input board (9) are matched pairs and must be changed together and not
mixed with others.
To remove the circuit boards (6 and 9) and display (4), first loose the cover locking (10) on the side not
marked "Field Terminals" then unscrew the cover (1).
WARNING:
The board has CMOS components which may be damaged by electrostatic discharges. Observe
correct procedures for handling CMOS components. It is also recommended to store the circuit boards
in electrostatic-proof cases.