The common methods used to measure the thickness of hot rolled steel coils include the following:

1. Ultrasonic Thickness Measurement:
   - This method uses high-frequency sound waves to determine the thickness of the steel coil.
   - An ultrasonic transducer is placed on the surface of the coil, and the time it takes for the sound waves to travel through the material and reflect back is used to calculate the thickness.
   - Ultrasonic thickness measurement is a non-destructive and accurate method, suitable for both online and offline measurements.

2. Micrometer Measurement:
   - This involves using a handheld micrometer caliper to physically measure the thickness of the steel coil at various points.
   - The micrometer measures the distance between the two parallel anvils or faces when the coil is placed between them.
   - Micrometer measurement is a simple and straightforward method, but it requires manual intervention and can be prone to operator error.

3. Laser Thickness Measurement:
   - This method uses a laser beam to measure the distance between the sensor and the surface of the steel coil.
   - The laser beam is projected onto the coil surface,  hot rolled steel coil ss400 factory  and the time-of-flight of the reflected beam is used to calculate the thickness.
   - Laser thickness measurement is a non-contact and highly accurate method, suitable for online monitoring and control applications.

4. Eddy Current Thickness Measurement:
   - This technique uses the principle of eddy currents to determine the thickness of the steel coil.
   - An alternating magnetic field is induced in the coil, and the changes in the eddy currents due to the coil's thickness are measured.
   - Eddy current thickness measurement is a non-destructive and reliable method, particularly suitable for online monitoring of coil thickness during the rolling process.

The choice of measurement method depends on factors such as the specific requirements of the application, the desired accuracy, the accessibility of the coil, and the integration with the production process.