Metal Double-Sheet Detector: Principles and Fault Analysis

1. Principle of Metal Double-Sheet Detection

The metal double-sheet detector is based on the Oersted principle and electromagnetic induction. T denotes the transmitter and R the receiver. When a target passes through the diffracted magnetic field produced by R and T, the receiver feeds back a signal strength to the host. Because the shielding area and thickness of the detected object vary, the returned signal strength differs, allowing the host to determine whether a single sheet or multiple sheets entered the sensing range.

Our current double-sheet metal detection product lineup includes:

 1. Double-Sheet Detector MDSC-1000B (standard model)

 2. Double-Sheet Sensor MDSC-1000L (mainly for the lithium battery industry)

 3. Double-Cover Detector MDSC-1000C (adds RS485 communication and two I/O channels to the double-sheet host)

 4. Material Double-Sheet Sensor MDSC-8000S (single-sensor)

 5. Metal Double-Sheet Detector 900E (Basic)

Distinguishing single from double sheets to protect downstream equipment from damage and reduce production loss is the basic purpose of metal double-sheet detectors. Typical applications include stamping presses, folding machines, bending machines and cutting machines.

2. Fault analysis

1) No display on power on

 Check whether the 24V power is correctly connected and whether supply is normal. Also check for loose terminals or blown fuses.

Summary: (1) power supply open circuit.

2) No input

When there is no input, start by checking the R and T probe wiring. Verify whether connections between detector and host are loose or disconnected; check whether R and T are aligned vertically or parallel; ensure R and T are not installed too high (greater than 50mm); and verify detection configuration.

Summary: (1) wiring to R/T probes is broken or damaged; (2) improper installation or detection settings.

3) Input present but no output

 Check the output terminal wiring and signal; measure the output pins for voltage difference.

Summary: (1) loose or fallen output terminal; (2) incorrect wiring method; (3) incomplete host program; (4) insufficient output delay time; (5) damaged output terminal.

4) Single sheet misreported as double (or double missed as single)

This category may be caused by overall structure, learning process, installation, actual sheet spacing and filter time, damaged R/T sensors, or incorrect host operation.

Summary: (1) learning error where single-sheet signal is as strong as or close to double-sheet signal; (2) incorrect feed position too close to the T sensor; (3) damaged R/T sensors; (4) increase filter time; (5) add dynamic learning adjustments.

When learning and actual detection positions cannot be ensured consistent, to prevent single-sheet misreports or double-sheet misses, during learning place a single sheet near the material center and move double sheets outward, ensuring the double-sheet signal is stronger than the single-sheet signal.

All other sensors and controllers can be freely matched except for M12 circular sensors; installation can be customized per customer requirements. When a lithium controller is connected to non-lithium sensors detection thickness may be significantly reduced; lithium sensors cannot be connected to non-lithium standard models. Lithium battery sensors carry very small current and standard machine currents may damage the M12 circular sensor head.