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Reject Mode Select
- After metal has been detected the metal detector output can be delayed by timing circuits
as described above. This works well for conveyor belts that move at a constant speed. In the case of variable
speed drives or conveyors that stop and start occasionally another method of timing is preferred. A pulse
counter circuit is the best alternative. The detector can be set to activate the outputs by time, by pulse count, or
manually. In the manual mode, the metal detector will stay in the reject position until an external button,
customer supplied, is activated.
Pulse Count
- In the pulse mode the reject timing is controlled by a pulse generator attached to one of the
conveyor pulleys. The generator creates 100 pulses per revolution of the conveyor pulley. The metal detector
has internal circuitry that will count the selected number of pulses before the reject device is activated. It will
also count pulses to set the operate time.
Reject On/Off
- Enables or disables all of the detector outputs. It is especially useful to have the reject device
disabled during the product set-up process.
Relay Configuration
– Relay outputs 1 & 2 are mechanical relays that have all three connections (NO, NC, &
COMM) supplied to the terminal strip. The reject device can be attached to the proper connections.
Relay outputs 3, 4, and 5 are solid state relays used for AC power. They can be configured as normally open
(NO) for devices that require power to operate or as normally closed (NC) for devices that require an
interruption of power to operate. Pressing the “RELAY CONFIG” will bring up the “RELAY CONTACT
SETUP” screen. After changing the configuration of the relays, you MUST press the “SAVE SETTINGS”
button to make the change permanent.
The metal detector is usually mounted on a conveyor that transports product to be inspected through the
aperture of the search head. A reject device such as an air blast or sweep arm is located some distance from the
metal detector. In order for the device to reject just the contaminated product, at the correct time, timing
parameters need to be set. In general, longer reject operate times result in more product being rejected, and a
greater insurance that the product containing the contaminating metal is diverted from the product stream.
Shorter operate times save product from the reject bin at the cost of a greater chance of contaminated product
not being rejected. In gravity type or pipeline applications it is usually recommended to keep the “delay” time
at “0” or as short as possible because the product is moving fast and the detector and the reject device are close
together. The “operate” time should also be short to minimized rejected product.
Setting the Timing of the Reject Device
To determine the settings for delay and operate timing, run a product with a metal contaminant sample through
the detector. Follow the hints on "
Tips for Setting the Reject Timing
" below.
If you change product, be sure that the delay and operate timing is appropriate for the new product size.
Tips for Setting the Reject Timing
1. Always set up reject times after determining the settings for a product.
2. Always run the packages in the same orientation as during actual production.
3. If the product is a package, put the metal sample at the mid-point of the package in the orientation that it will
go through the metal detector.
