Structure and function
The hot sheet thickness measuring instrument basically consists of the following four modules:
- Measuring head
- Feed unit
- Control cabinet with manual control panel
- Electronic evaluation and display unit
The feed unit has the task of moving the measuring head from the park-position to the measuring position and from the measuring position to the park-position.
A three-phase current worm gear motor with stop brake serves as a feed drive. The thrust rod is driven positively by a rack and pinion.
The thrust rod consists of a hardened, chrome-plated tube with an outside diameter of 80 mm. There is a rack all along the underside for the drive.
The measuring head is clamped to the front end of the thrust rod. After loosening the locking screws the head can be swung and therefore set exactly at a right angle to the roller bed.
The front part of the measuring head contains the measuring probes for determining the sheet thickness. The measuring probes are driven pneumatically by filling the entire measuring housing with compressed air. The measuring probes are guided in ceramic rings at the outlet openings. There is a defined gap between the respective ceramic ring and the probe through which compressed air flows continuously during the active measurement. This creates a permanent air flow through the measuring housing to cool the measuring electronics. The air flow is dimensioned so that radiation and contact heat to which the system is exposed externally is totally dissipated.
After every active measurement a reference run is performed in the park position in which the measuring probes are set exactly on top of each other. This ensures that thermal deformations of the measuring head housing or long-term wear on the probes cannot lead to measuring faults. After every MEASURE START COMMAND the last reference value before opening the measuring head is used for the following measurement. This continuous reference function ensures a high measuring accuracy and measuring certainty.
The arrangement of the measuring electronics directly in the measuring axis prevents measuring faults from occurring, e.g. due to tilting. The sheet thickness is determined by forming the difference between the two contact positions and the zero position (probe touching directly).
