Siemens UM344-2 user manual Possible Cause Corrective Action

CALIBRATION AND MAINTENANCE UM344-2

TABLE 6.7 Symptom - Output Current Fixed Below Scale

at Approximately 3.84 mA

POSSIBLE CAUSE	CORRECTIVE ACTION
Loop supply voltage less than 12 Vdc at transmitter	Replace power supply.
SIGNAL +/- terminals.
Thermocouple Burnout (if Downscale protection) or	Refer to Figure 4-13 and perform a standard open circuit
thermocouple extension wire(s) open.	(thermocouple) check between transmitter terminals #1
	and #3.
Thermocouple wires have polarity reversed.	Consult thermocouple wire tables (or Table 6.1) and
	determine color code for positive and negative wires.
	Check wire connections at transmitter terminal
	compartment and at thermocouple head if thermocouple
	is remote mounted.
Shorted thermocouple extension wires (due to insulation	Special Time-Domain Reflectometer (TDR) measurements
failure) between remote mounted thermocouple and	can be used to locate the short; otherwise, a visual
transmitter.	inspection of the length of wire must be made to locate
	the short.
The transmitter will read the temperature at the short
(junction) which, if 3% less than the configured Zero
range value, will force the output current to a maximum
low value of 3.84 mA.
Incorrect lead connections on 3-wire RTD.	Refer to Figure 4-13 and check for correct sensor wiring.
Open RTD lead on double -lead side of 3-wire RTD.	Refer to Figure 4-13 and perform continuity check
	between RTD wires connected to transmitter terminals #1
	and #2 to confirm open circuit.
The single side RTD lead is shorted to one of the double -	Refer to Figure 4-13 and perform continuity check
side RTD leads (RTD shorted out).	between RTD wires #1 and #3 to confirm shorted RTD
Temperature is less than Lower Range Limit (LRL).	Re-range transmitter. Refer to Section 5.

TABLE 6.8 Symptom - Output Current Fixed Above Scale

at Approximately 21.8 mA

POSSIBLE CAUSE	CORRECTIVE ACTION
Thermocouple Burnout (if Upscale protection) or	Refer to Figure 4-13 and perform burnout check on
thermocouple extension wire(s) open.	thermocouple and continuity check on wires
	between transmitter terminals #1 and #3 to isolate
	the fault.
RTD element open or, if RTD is remote mounted,	Refer to Figure 4-13 and perform continuity checks
return wire to transmitter terminal #3 is open	on RTD and RTD return wire to transmitter
	terminal #3 to isolate the fault
Temperature is greater than Upper Range Limit	Re-range transmitter. Refer to Section 5.
(URL).

6-24 September 1995