What is a thermocouple wire? Thermocouple wires are a special wires that are made up of two dissimilar metals that when coupled together will generate a voltage signal in response to a change in temperature where it is exposed to.

Thermocouple wires are widely used mostly in all fields of a processing or manufacturing plants whether directly or indirectly (permanently installed or used just a probe) used in a process.

I usually see thermocouples used in equipments and devices like Oven, chambers, liquid baths and surface metal plates to measure and monitor temperatures. Their ability to be deformed, routed and shaped in different ways are some of its characteristics that makes them a good choice as a temperature sensor.

Regardless how it is used, thermocouple wires should be calibrated and checked for physical damage or any deteriorations, because these can cause errors and out of tolerance measurement results.

This procedure is applicable to all types of thermocouples but we will concentrate only on type K for this presentation.

In this post, I have presented 2 calibration methods for themocouple wires:
1. Method 1: Open  and Welded End theromoucple wires
2. Method 2: Both Ends Open thermocoupe wires

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.

Calibration Method 1: For Open and Welded End Thermocouple wire

This is for a thermocouple with an open and welded end. This is   accomplished by comparing the simulated temperatures generated from  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:

• 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.