I believe most of us are familiar with ovens. Once heard, we think of it as equipment used for heating. This can be what most of us know, but for those exposed in manufacturing zones, a few usages of ovens are for quicker drying, sterilization, and reliability testing.
For example, in semiconductor industries, Oven tests the strength of a solder joint in a chip at a given temperature. Some laboratory apparatus used for testing products inside the lab are being dried and sterilized using the Oven in the food industry.
As we see, usage of ovens is fundamental where a precise temperature ought to be kept up. This accuracy can be determined through calibration. This blog will share how to calibrate an electric oven employing an advanced thermometer and a thermocouple wire. The blog will display a 3-point calibration set up in an electric oven with an analog temperature controller. Although this calibration will be conducted on a basic and small electric Oven, this method is appropriate to most single-layered industrial ovens used within the manufacturing field and the digital Oven, the more advanced type.
Why Should You Calibrate Ovens?
The short answer is to guarantee the precision of the temperature interior of the oven enclosures. Most electric ovens are mechanically operated where each part experiences stress, particularly the thermostat section. This section is where the sensor is attached. The thermostat is operated by a dial knob that’s designed to be triggered to switch on and off once it detects the desired temperature settings. When this sensor is not accurate, the desired temperature will not be produced, influencing the quality of your product.
As usage is at maximum, the sensor loses its accuracy or efficiency, and therefore, a calibration should be performed to detect such in-efficiency or in-accuracy.
Temperature calibration is also performed after a repair is done to verify its accuracy.
Moreover, calibration is performed to determine the exact position and location of items placed inside the oven where the temperature is at a minimum or maximum to create proper adjustments or positioning of products.
Electric Oven Calibration Procedure
We calibrate an electric oven to determine the accuracy of the temperature it produces at a specified set point or set value.
Other reasons we perform calibrations includes:
- To determine the stability of temperatures.
- To determine inhomogeneities or uniformity of readings.
- To determine the most accurate or appropriate locations inside the chamber.
- To determine the accuracy of a particular test point as per-user settings.
Oven temperature calibration is simple, but it may be time-consuming when calibrating more than one test point. The need to stabilize it before taking the reading may make the process slow. Moreover, stabilizing times are not the same for every oven. Some ovens take an hour to reach the test point before stabilization.
The basic procedure to calibrate an electric oven is to compare the generated temperature of the oven through the set value in the dial knob to the reading of the reference standard, a digital thermometer with a thermocouple/RTD wire the sensors. Possible to use high temperature wireless thermo-shield data logger.
- Warm-up time (Unit Under Calibration): At least 1 hour for proper stabilization
- Room Temperature: 23± 5°C
- Room Humidity: 50 ± 30%
- Perform 3 trials for each point or range
Reference Standard To Be Used
- Calibrated reference thermometer.
- Thermocouple/RTD wires (capability to withstand a temperature of at least 300 deg C).
- Thermo-hygrometer– for temperature and humidity
- Cleaning materials.
Oven Calibration Set-Up
Open the oven and insert the sensor wires inside. For standard calibration, distribute the cables in three locations: one in the center, the middle right, and the middle left side, respectively. The middle sensor will be the reference sensor.
The more sensor wires, the better. This way, we can determine a good uniformity reading.
5pcs is the optimal number of sensors for an oven this size. The sensors should be evenly positioned across the four middle areas of each side of the oven and one at the middle.
A temperature recorder with five or more channels is the preferred reference standard to be used. This setup can be left alone to while it records the readings automatically.
- Take proper care and safety precautions; ovens generate a high temperature which can cause burns and damages.
- Check the electric ovens for any visual defects that can affect their accuracy. Check the fan, the heating elements, and the thermostat dial functionality. Discontinue calibration if any defect is noted.
- Prepare the measurement data sheet and record all necessary details or information (Brand, Model, serial #, etc.).
- Determine the electric oven range, divide the range based on the scale, and choose at least 3 test points.
- Follow the setup above.
- Turn on the electric oven and set the temperature to set point 1, starting from low to high temperature.
- Wait for the readings on display to stabilize (approximately 20 min).
- Record readings on the datasheet. Fill up Trial 1 for sensor 1, trial 2 for sensor 2, and trial 3 for sensor 3.
- Turn to the next set point and Continue steps 7 and 8 until all ranges are finished.
- For stability, select the mid-range and determine the highest and lowest reading within 30 min. time interval
- Check readings if within the accuracy defined by the manufacturer or as per user requirements, for example, accuracy = ±2 °C. If the readings are already within limits, update the corresponding record, do labeling and sealing; otherwise, do necessary repair or adjustment.
Through the calibration process, we are able to determine errors and perform adjustments. To get the correction, just subtract the average standard reading and the oven knob setting. Use the correction for each use of the oven setting to compensate for the error. Typically, applicable in case the oven is not adjustable. Measurement uncertainty can be assessed by advanced calculations. Based on the calibration result, there is a correction of 0.5°C, which means that for every setpoint of 200, add a 0.50 as the correction factor.
I have presented here a simple procedure to calibrate an electric oven by using a high-temperature wire sensor. Make sure to use the right thermocouple/RTD wires to avoid burning its coating.
Sigma Sensors (TCL) GmbH