How to Self-Test a Furnace Temperature Sensor

Comparing a furnace temperature sensor to a typical thermocouple, confirming the temperature difference through multi-point temperature measurements, and examining anomalous drift through previous furnace temperature curves are the fundamental steps in self-testing a furnace temperature sensor. The following are the precise operating steps:

 

1. The Most Direct Standard Thermocouple Comparison Method

Procedures

Operating Guidelines

Get the standard equipment ready.

Acquire a high-precision thermometer and a standard platinum-rhodium thermocouple with an accuracy of ±1°C that has been metrologically validated.

Placement in Parallel

To ensure constant heating conditions, firmly connect the regular thermocouple and the sensor under test in parallel and position them in the furnace's medium-temperature zone.

Warming up to 580°C

After heating in accordance with standard procedure, wait at least half an hour for the temperature to stabilize.

Examining Comparisons

Note both the control system's displayed value and the standard value. The sensor is incorrect if the variance is more than ±5°C.

Advice: To prevent the workpiece from absorbing heat and disrupting the temperature field, this can be done in an empty furnace.

 

2. Verification of Multi-point Temperature Measurement (Judging Uniformity)

Place at least three separate portable thermocouples in the furnace's corners, top, middle, and bottom;

Increase the temperature to 580°C and maintain it there, noting the temperature at each stage;

A sensor or furnace body issue is indicated if the greatest temperature differential is more than 5°C;

Determine whether sensor error is the cause of the error by combining it with the control system information.

For instance, the control system shows 580°C, while the measured bottom layer is only 568°C, a 12°C difference that necessitates quick calibration.

 

3. Method of Historical Curve Comparison Analysis (Trend Identification)

Use the same procedure to retrieve furnace temperature curve records from the previous three to five times;

Examine the following irregularities:

The temperature must be reached either much sooner or later;

persistent drift or variation greater than ±5°C throughout the holding period;

a notable shift in the heating slope (for example, from 150°C/h to 200°C/h);

A trend shift suggests that the sensor is aging or malfunctioning.

It is advised to create curve archives for tracking long-term trends.

 

4. Determine whether calibration is required as soon as possible.

Description of the Signal

Hardness range > 2 HRC: This could be a sign of an inaccurate temperature measurement once material and furnace loading factors have been ruled out.

Frequent brittle fracture or softening: Actual temperature departure is indicated by performance fluctuations even when the process remains steady.

Following equipment maintenance: Re-verification is required following the replacement of sensors, temperature controls, or heating elements.