Avery Berkel CX20 SERIES, Service Manual

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23 — RS232 Interface PCB (CX20 W)
23–5 CX20/CX30/CX34 Service Manual
23.2.4 Scale in control signal (control interface version 2
only)
This signal is an output from the scale to the wrapping machine to show the
scale is in wrapping mode and the wrapping machine needs to take control of
the wrapping system. The scale software writes a 0 to the DUART RTS channel
B pin to assert ”Scale In Control” true.
To drive these isolated signals the interface circuit makes use of the ULMA +24V
to act as the current source.
23.2.5 Analogue interface
As the weighing platform is remote, an LC filter is included on the RS232
interface PCB that filters external noise.
23.2.6 ”Wrapper Start” relay control
For the older style of wrapper the RS232 interface is not used, instead a relay
closure initiates the wrap cycle. The main PCB cash drawer output is used to
close the relay. To do this the microprocessor on the main PCB checks for a
steady weight and also label removed. When this condition is true the scale
signals the printer microprocessor to start the wrapper. The printer
microprocessor then switches on a transistor to close the relay on the RS232
interface PCB.
The relay current is approximately 10mA, the contact closure time is 100ms.
The LED D2 (on the interface PCB) flashes momentarily when the wrapper
signal is fired.
23.2.7 Label taken detection
A reflective photocell is used to determine whether the previous label has been
removed. An LM393 comparator is used to generate a logic output from the
phototransistor collector signal. As the RS232 interface PCB has to work with
no changes to the main PCB the only main PCB input is in a switch matrix. This
means that a ’voltage free’ contact closure is needed, hence relay RL2 is used.
LED D3 gives a visible indication of what state the photocell is in, LED
illuminated means a label is present, in this state RL2 will be closed.