Thermocouple Test Procedure

1-   Thermocouple Test (“T”, “J”, “K” or any other type)

Procedure	General Procedure for all stations.
Title of Job	Annual Maintenance Check & Calibration
Manpower	Instrument Technician Using PPE (Personal Protective Equipment)
Safety Document	Maintenance Work Permits. & SCC (Safety Clearance Certificate) If Required
Tools    /    Special Tools	I &C Tool Kit + any special tools (if Required)		Test Equipment
Test Equipment:	Note: Select test equipment according to the max. Range of Thermocouple. 1– Ice pot ( For “0” degree C) 2- Boiling water (For 100 degree C) 3- Low Temperature Bath (Dry block) (From Ambient to 200 Degree C) 4- High Temperature bathe (Dry block) (From Ambient to 600 Degree C) 5- Digital precession temperature Calibrator. 6– Multi function multi-meter (AVO Meter)		Digital   Temp.   Bath   & Calibrator
Stores & Materials	Cleaning spray, brush and cloth

Job Description
Process	Steps	During  Maintenance
Isolation	1	Open the cover of thermocouple. Remove the wires by the core identification and insulate all wires by insulation tape (Ensure it isn’t in contact with each other, short circuiting or producing any earth). Remove the fittings, brackets, vibration suppressers etc. (If available).
&
Removal
	2	Remove thermocouple from thermo well carefully by opening upper nut of thermowell.
		Note:  Thermo  well  should  not  be  removed from the pipe until there is a problem.

	3	Thermo well should be removed if there is leak or need cleaning due to scaling, dirt deposits and sediments. After cleaning well and scaling is removed, fix back with rapping new Teflon tap properly. Carefully tight so much that there should be no leak from threads of thermo well.
	4	Carry out the thermocouple external cleaning, using a brush and approved cleaning spray to remove contamination or solid particles.
	5	Inspect the thermocouple for external physical damage, general appearance & fitness. (Check whether cover seals are intact).
Preparation	6	Write the all detail of thermocouple, Tag No., Temperature range showing on the indicator in control room, Type of thermocouple (T, J, and K), Service and Unit No. in the Test sheet.
	7	Test of Ohms meter: To check continuity, selects the knob of multi meter on ohms or symbol of ohms (Ω). To confirm that multi meter is working in good condition. Touch both wires with each other. If it shows “0” ohm. When opening wires shows (OL) or infinity. This means multi meter is healthy and can be used.
	8	Continuity test of thermocouple: Check the continuity of thermocouple by ohm meter by connecting both wires with both terminals of thermocouple. If It shows “0” ohms or near to zero ohms. This shows that thermo couple is healthy
	9	Unground test of thermocouple: If thermocouple is un-grounded then connects one wire of ohm meter with body of thermocouple and other with one terminal. It should show infinity resistance or OL (over limit). Same should do with 2nd terminal.
	10	Set up test equipment as per the Diagram shown in picture. Remove cover of thermocouple as required to connect up the test equipment to Terminals. Confirm the polarity of test equipment is connected with right polarity of thermocouple.
Test Procedure	11	There are two methods of test.
		1)  1st Method (T/C Output mV test by Multi meter).
		2)  2nd    Method    (Temperature    test    by    Digital	precession
		temperature Calibrator)
	12	1st Method (mV test by Multi meter)   Select the knob of multi-meter on the “mVDC” and connect both wires to both terminals according to the polarity.
	13	Insert thermocouple bulb in the ice pot. Give some time to stabilize till stop changing mVDC output of thermocouple on multi meter.

	14	Note down “mVDC” and compare with standard chart matches with the type of T/C (T, J, and K Type). It should match with “0” degree C.
	15	Now switch on the temperature bath and set a temperature setting on it (according to the thermocouple type) and start heating the thermocouple bulb. Note: Set  temperature should  not  be more than thermocouple type or temperature shown on the indicator in control room). If set value is less than the max. Value is better and safe.
	16	Max ranges of diff. type of thermocouples.
	17	Watch on the multi meter. It starts to increase “mVDC”. Let stabilize the temperature which is set on the temperature bath & Note down the setter value.
	18	Now we can match this “mVDC” value with the standard temperature chart value and confirm that how much temperature will be acting on the thermocouple sensor bulb.
	19	If “mVDC” is matching with the temperature shown in the standard chart related  to  the  thermocouple  type,  means  thermocouple  is  in  good condition.
	20	2nd     Method   (Temperature   test   by   multi-function   Digital   precession temperature calibrator. Connect Digital precession temperature calibrator with thermocouple, which can show direct temperature on the meter and connect both wires to both terminals according to the polarity.
	21	Switch on the calibrator and select T/C on the calibrator and then select the type of thermocouple, like “J type” “T type” or “K type”.
	22	Insert thermocouple sensor (Bulb) in ice pot and wait to stabilize temperature at 0 C.
	23	Watch on the temperature calibrator. It starts to decrease temperature. Let stabilize up to “0” degree. If it shows “0” degree. Means thermocouple is healthy.
	24	Now  insert  the  thermocouple  sensor  in  the  temperature  dry  bath  and switch ON the bath. Set 100 C or 200 C temperature on the bath.
	25	Watch on the Digital precession temperature calibrator. It starts to increase temperature. Let stabilize the temperature on the calibrator & compare with the set temperature on the bath. Both temperatures should be same. Means thermocouple is healthy and can be used.

	26	Note down the set temperature and shown temperature on the temperature calibrator in the test sheet.
	27	The thermocouple test procedure should be inspected by MEW Inspector and  Quality Inspector  for witness  and  record  these values  to sign the certificate after completion of job.
Completion	28	Once the test is completed, remove the test equipment and clean the tested device.
	29	Fix back T/C to its position and ensure that connection are not cross fitted with thermo well that can damage threading.
	30	Reconnect the Thermocouple wires on its original terminal according to the core identification. Fix the cover properly and clean the tested device.
	31	Check the condition of the fittings, brackets, vibration suppressers etc. Repair or replace as found necessary
	32	Check  for  leakage  of  thermocouple  from  the  thermo  well  during commissioning.
	35	Complete the check and test sheet and handover to the concerned MEW I&C Engineer for inspection and signature.