Thermocouple Wire Calibration Procedure – Type K Thermocouple

with 5 Comments

Thermocouple wires are widely used mostly in all fields of a processing or manufacturing environments whether directly or indirectly ( permanently installed or used just a probe) used in a process. However it is used, thermocouple wires should be calibrated and check for physical defects.This procedure is applicable to all types of thermocouples but we will concentrate only on type K for this presentation.

Objective:

To define verification procedure Of thermocouple wires or probe using a Metrology Well As the reference standard and  Fluke 754/1524 as the indicator. I will present here 2 methods in calibrating a thermocouple wire.

 

Calibration Method 1:

 

type-k-thermoocuple-wire-welded
Typr K thermocouple wire with welded end and open end

fluke-metrology-well-and-fluke-1524

This is for a thermocouple with an open and close end,  accomplished by comparing the simulated temperatures generated from Fluke Metrology Well, which is the reference standard. The wire or probe is inserted on the Metrology  Well where the Unit Under Calibration(UUC),  is being compared to.

Requirements:

  • Warm-up time (UUC): At least 1 hour for proper stabilization
  • Temperature:   23 +/- 5 deg C
  • Humidity:         50 +/- 30%
  • Perform 3 test points for each range
  • Measurement Data Sheet (MDS)

Reference Standard and Equipment:

thermocouple-mds
Sample Measurement Data Sheet (MDS)
  • Fluke Metrology Well
  • Thermohygrometer – for environment monitoring
  • Fluke 1524  – for display
  • Cleaning materials

Calibration Procedure:

  1. Observe proper care and safety, Metrology Well generate a high temperature which can cause burn and damage.
  2. Check the thermocouple wire for any visual defects that can affect its accuracy. Discontinue calibration if any defect is noted.
  3. Clean the thermocouple wire with a soft cloth.
  4. Prepare the measurement data sheet (MDS) and record all necessary details or information ( Brand, Model, serial #, etc).
  5. Determine the range of the thermocouple wire or the user range ( an example is from  250  to 700 deg Celsius), choose at least 5 test point.
  6. Turn on the Well and set to the desired temperature, starting from low to high temperature.
  7. Once the temperature of the Metrology well has stabilized, carefully insert the welded end of the thermocouple on the holes in the well.  There are different sizes of holes so choose the one that fits properly to ensure maximum heat absorption and accuracy.
  8. Then insert also the open end with a connector to the indicator and set the required thermocouple type which is type K.
  9. Wait for the display to stabilize ( approximately 10 min) then get the reading. Record readings on the MDS.
  10. Continue steps 4 to 7 until all ranges are finished.
  11. Check readings if within the accuracy defined by the manufacturer, for type K , accuracy = +/-(0.75%) of reading.
  12. If the readings are already within limits update the corresponding record, do labeling and sealing and issue to the owner, otherwise, do necessary repair or adjustment.

Calibration Method 2:

 

20160901_095452

This is for a thermocouple wire with both ends open,  accomplished by comparing the simulated temperatures generated from Fluke 5522a calibrator, which is the reference standard, to the display of the indicator ( Fluke 754 or equivalent), where the   Unit Under Calibration  (UUC) is connected.

type-k-thermocouple-wire
Type K thermocouple wire with both ends open

 

Requirements:

  • Warm-up time (UUC): At least 1 hour for proper stabilization
  • Temperature:   23 +/- 5 deg C
  • Humidity:         50 +/- 30%
  • Measurement Data Sheet (MDS)

Reference Standard and Equipment:

  • Fluke 5522a calibrator
  • Thermohygrometer – for environment monitoring
  • Fluke 1524  or Fluke 754- for display
  • Cleaning materials
  • Connector/adaptor

Calibration Procedure:

  1. Allow the temperature of the UUC to stabilize at room temperature.
  2. Check the battery and fuse of the indicator, replace if necessary.
  3. Record necessary details on the Measurement Data Sheet (MDS)( Brand, Model, Serial, etc.)
  4. Check for any physical or functional defect , discontinue calibration if defects are noted. Inform owner immediately.
  5. Clean the thermocouple wire with a soft cloth.
  6. Determine the range of the thermocouple wire or the user range ( an example is from  250  to 700 deg Celsius), choose at least 5 test point.
  7. Turn on the Fluke 5522a calibrator and connect the thermocouple as shown in the Figure.
  8. Select the thermocouple type on the menu of the calibrator( Fluke 5522a) and indicator (Fluke 754)
  9. Enter desired temperature values, wait for the display to stabilize ( at least 1 min for every setpoint) then get the reading. Record readings on the MDS.
  10. Continue steps 8 to 9 until all ranges are finished.
  11. Check readings if within the accuracy defined by the manufacturer, for type K, accuracy = +/-(0.75%) of reading.
  12. If the readings are already within limits update the corresponding record, do labeling and sealing and issue to the owner, otherwise, do necessary repair or adjustment.
  13. end.

Please visit Thermocouple Calibration Setups for additional explanations.

Thank you for visiting my site, please share and comment.

Edwin

5 Responses

  1. Jhamiea al khathani
    | Reply

    Do u have any conversion table for Type k From Temperature to millivolts?

  2. edsponce
    | Reply

    I Just received a comment regarding a thermocouple that has a burned insulation after it was soaked in a metrology well with a 450 deg C temperature for calibration.
    Below are my responses. Hope that it would add additional information.
    ________
    Below are the reasons why your thermocouple insulation was burned:
    1. Thermocouple insulation is not designed for the temperature you are using. Some insulations can withstand only upto 150 deg C. Look for a braided type ( or other types) insulated thermocouple wire.

    2. Check the type of thermocouple you are using and verify its temperature range. Most Thermocouple can measure upto 1000 Deg C but it is dependent on its insulation and thickness of the wire.

    3. Check how the thermocouple is being used in your process, some thermocouples are used as a surface sensor so the procedure for calibration is not matching. check other related procedure here in my blog.

    4. You may use an extension probe as the main sensor to be inserted in the metrology well.
    Extension probe is a sensor probe to be connected in the thermocouple which is almost similar to a solid metal bar.

    HOpe this help.
    Best regards,
    Edwin

  3. md ahamad
    | Reply

    Hi
    can i know the calibration frequency of thermocouple bacouse as i seen in ASME standard there is no any electrification regarding validation plase send me the standard code and reference

    • edsponce
      | Reply

      Hi Mr. Ahamad,
      Thank you for visiting my site. Calibration frequency, as far as I know, it has no standards set to be followed. Most calibration frequencies are suggestions and recommendations. These suggestions and recommendations are based on the experiences of most users. I experienced about thermocouples having a calibration frequency starting from 3 months going 6 months to 1 year.
      But this is based on how the thermocouples are used, the quality of the thermocouples and many more other reasons. And all of these must be properly documented. Please check below guide about this.
      Please check this standard from GSO. GSO OIML D 10:2010 – Guidelines for the determination of calibration intervals of measuring instruments.
      Regarding the validation, this is based on company policy or procedure, there should be a planned or scheduled execution of validation and/or verification. You may check ISO 9001:2015 under clause 7.1.5 and ISO 17025:2017 Clause 7.7 related to monitoring the validity of results.

      I hope this helps.
      Edwin

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