Resistance Temperature Detector (RTD) Test Procedure

1-   Resistance Temp. Detector (RTD) (Pt100Ω) or any other type, 2wire, 3wire or 4 wires.

Procedure	General Procedure for all power plants and refineries instrumentation.
Title of Job	Annual Maintenance Check & Calibration
Manpower	Instrument Technician Using PPE (Personal Protective Equipment)
Safety	Maintenance Work Permits. & SCC (Safety Clearance Certificate) If Required
Document
Tools/     Special	I &C Tool Kit + any special tools (if Required)		Test Equipment
Tools
	Note: Select test equipment according to the max. Range of RTD. 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)
Test Equipment:			Digital   Temp.   Bath   &
			Calibrator
Stores                & Materials	Cleaning spray, brush and cloth

Job Description
Process	Steps	During  Maintenance
Isolation	1	Open the cover of RTD. 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 RTD from thermowell 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 it needs cleaning due to scaling, dirt deposits and sediments. After cleaning well and scaling is removed, fix back with wrapping new Teflon tap properly. Carefully tight so much that there should be no leak from threads of thermo well
	4	Carry out the RTD external cleaning, using a brush and approved cleaning spray to remove contamination or solid particles.
	5	Inspect  the  RTD  for  external  physical  damage,  general  appearance  & fitness. (Check whether cover seals are intact).
Preparation	6	Write the all detail of RTD, Tag No., Type of RTD, Temperature range showing on the indicator in control room, Service and Unit No. in the Test sheet.
	7	Test of Ohms meter: To check continuity, select the knob of multi meter on ohms or symbol of ohms (Ω). To confirm that multi meter is working in good condition: touch both wire with each other and it showing “0” ohm and if separated it shows (OL) or infinity it indicates multi meter is “OK” to be used.
	8	Continuity test of RTD: Check the continuity of RTD from ohm meter by connecting both wires to terminal 2 & 3 having black wires. It should show “0” ohms resistance. Means reference wires are in good condition. Now connect red wire to terminal 1 & 2 or 1&3 and see the resistance, it should read nearly 110~112 ohms. Means 100 ohms are for PT100 + 10 ~ 12 ohms for ambient temperature) means RTD is in good condition and can be test. Note:   If resistance in between terminal 1&2 or 1&3 shows more than 110~112 ohms or kilo ohms or mega ohms or “OL” means RTD is defective. Resistance in between terminal 2&3 (Black wires) shows more than “0” ohms or kilo ohms or mega ohms means. RTD reference wire is defective. RTD should be replace with new RTD)
	9	Unground test of RTD: If RTD is un-grounded then connects one wire of ohm meter with body of RTD and other with each terminal one by one. It should show infinity resistance or OL (over limit).
	10	Set up the test equipment as per shown in this picture. Remove cover of RTD as required to connect up the test equipment to the terminals. Confirm the polarity of test equipment is connected with right polarity of RTD.

Test Procedure	11	There are two methods of test. 1)  1st Method by Ohm test  (Pt-100 ohms  3 Wire) 2)  2nd  Method  by Digital precession temperature Calibrator (Pt- 100 ohms  3 Wire)
	12	1st Method by ohm test  (Pt-100 ohms  3 Wire) Select “Ω” on the multi meter. Connect red wire of multi meter to  terminal 1 (white / red wire) of RTD and connect black wire of multi Meter to terminals 2 & 3 (black wires) to both terminals simultaneously.
	13	Note the value of resistance at ambient temperature. It will be PT-100 Ohms + resistance against ambient temperature and compare this total resistance with standard temperature chart. (Pt-100 Ω).
	14	Insert RTD bulb in the ice pot. Wait for some time to stabilize.
	15	Resistance on the ohms meter starts decreasing it will reach 100 ohms. Note down resistance showed on the ohms meter and compare with standard temperature chart. It should be “100 ohms” equal to “0”degree C same as ice temperature.
	16	Insert RTD bulb in the temperature dry bath. Now switch ON the temperature  bath  and  set  a  temperature  150C  setting  on  it.  Now  start heating the RTD sensor. Note: Set temperature should not more than the Max. Range of Pt100 ohms. (Max. Range of PT-100 is 260C.)
	17	Wait to stabilize the temperature on the temperature bath.
	18	View reading value on the multi meter. It starts increasing resistance value, when it reaches on the set temperature and there is no change in resistance. Note down the resistance value.
	19	Now we can match “this value” with the standard temperature Pt100 chart and confirm temperature on the RTD sensor bulb. Resistance of Pt-100 should be matched with set temperature.
	20	If “Resistance” is according to the temperature shown in the chart, means RTD is healthy and in good condition.
	21	2nd    Method:  Temperature  test  by  multi-function  Digital  precession temperature calibrator. Select RTD Pt-100 ohms on multifunction temperature calibrator which can show direct temperature on the temperature calibrator.
	22	Connect Digital precession temperature calibrator with RTD, connect red wire of digital temperature calibrator to terminal 1 (white/red wire) and black wire of calibrator to the other two terminals of RTD simultaneously.
	23	* Note down the ambient temperature on the calibrator before test start. After connecting digital precession temperature calibrator with RTD and wait  to  stabilize  ambient  temperature.  This  tested  temperature  should match with ambient temperature.

	24	Insert RTD sensor (Bulb) in ice pot and wait to stabilize temperature at 0 C on the temperature calibrator.
	25	Analyze  temperature  calibrator,  it  would  decrease  temperature.  Let  it stabilize up to “0” degree as ice temperature.
	26	Now insert the RTD sensor in the temperature dry bath and switch ON the bath. Set 150 C temperatures on the bath.
	27	Watch on the Digital precession temperature calibrator. It starts to increase temperature. Let stabilize the temperature as set on the bath.
	38	Now compare the temperature with the set temperature on the bath. Both temperatures should be same. Means RTD is healthy and is in good condition.
	29	Note down the set temperature and shown temperature in the test sheet. Both temperatures should be same.
	30	The RTD test procedure should be inspected by Inspector and Quality Inspector for witness and record these values to sign the certificate after completion of job.
Completion	31	Once the test of RTD is completed, remove the test equipment and clean the tested device.
	32	Fix back RTD to its position and ensure that connection are not cross fitted with thermo well that can damage threading.
	33	Reconnect the RTD wires on its original terminal according to the core identification. Fix the cover properly and clean the tested device.
	34	Check the condition of the fittings, brackets, vibration suppressers etc. Repair or replace as found necessary
	35	Check for leakage of RTD from thermo well during commissioning.
	36	Complete the check and test sheet and handover to the concerned I&C Engineer for inspection and signature.