The MC-PLC board is an analogue and digital signal processor designed for use in all applications normally fulfilled with PLC systems, plus it offers the considerable advantage of having a processing speed of at least 10 times superior. With the MC-PLC board you can therefore manage applications in which the PLC would not be precise due to the impossibility to follow short signals.

In the basic version, the board offers the following resources:

• 8 opto-isolated two-way inputs (NPN or PNP), some of which can be associated with special functions (management of signals with duration of a few millionths of a second or metering of frequencies and/or times)
• 8 NPN outputs (open-collector) with max. current 100mA (non-inductive)
• 3 analogue inputs (8 bit)
• A serial interface RS232 (or RS485 in alternative) for connecting a PC or a serial printer.
• A non-volatile memory (EEPROM) of 128 bytes for saving data and configurations (expandable on board up to 32 Kbyte)
• 2 synchronous serial lines for expansion modules (supplementary inputs/outputs, display units, high precision digital/analogue converters and analogue/digital converters, memory expansion etc.)

* The number of outputs available is bound to the use or otherwise of the synchronous serial ports.

Examples of use of the logic board MC-PLC

EXAMPLE 1: High speed bottling line with double substratum presence control.

In a bottling and labelling plant of bottles of alcoholic beverages, simultaneous presence of bottle B and the label E to be applied on the cap had to be controlled. Following positive result of the control phase, the system had to start the programmer for sections of adhesive to control gun P, causing hot glue to be placed on the cap of the bottle.

The problems to be overcome to fulfil this type of control were 3:

• The 2 photocells F1 and F2 were never activated simultaneously.
• The speed of the line could have varied considerably (production could have changed between 3000 and 18000 bottles/hour).
• Centring precision of the spot of adhesive had to be very high (the spot had to be placed in the centre of the cap with a tolerance of just a few mm)

Solution: the MC-PLC board was used to extend the activation time of photocells F1 and F2, taking it to such a value to allow the simultaneous presence of the 2 signals.

When the simultaneous condition was met, the MC-PLC sends the activation command of the spraying cycle to the programmer.

The high variability in the speed of the line made it impossible to keep the times of the 2 photocells constant, which, if set for the production rate of 3000 bottles/hour, were too long for that of 18000 bottles/hour (if even just one bottle was missing, the time would not expire, causing the gun to activate accidentally).

For this reason, the times associated with the 2 photocells were bound to the speed of the line by reading the encoder already installed (the rise in speed proportionally reduces the duration of the times of the photocells).

To make it easier to program the system, the 2 minimum and maximum speed values were entered by means of a teach-in function (reading and saving of the current speed). Thanks to the high processing speed of the MC-PLC board, all these functions can be managed simultaneously, guaranteeing the perfect centring of the spot of adhesive.

The illustration shows:

B = Bottle on which the label is to be applied.
F1 = Bottle presence reading photocell.
F2 = Label presence reading photocell.
P = Hot-melt gun
E = Label to be applied
CE = Loader with labels
D = Distributor that takes the label from the CE loader to the application position E

EXAMPLE 2: Feedback control of the quantity of additive for a plastic film extrusion line.

In a system made up of 3 plastic film extrusion lines (the illustration shows just one of the 3 lines), the quantity of hot additive to be mixed with the PVC to be extruded had to be controlled, bearing in mind the quantity set by the operator and the extrusion speed.

For reasons of precision, the amount of additive really dispensed also had to be controlled, compensating the speed of the pump and managing any flow alarms if compensation was not possible.

Alarms from the extrusion line and from the additive containment tank also had to be managed, displaying all the anomalies and operating options on the operator panel.

The meter used is the gear type with encoder.

The speed of the additive pump is adjustable with a standard analogue signal 0-10V.

The speed of the extrusion line is given by a standard analogue signal 0-10V.

Solution: the system was fulfilled using an electronic section repeated for each of the 3 extrusion lines.

Each section consists of an MC-PLC board, combined with an interface with analogue output 0-10V, capable of managing the line and controlling all the signals.

The speed of the pump is set considering the data bound to the speed of the extrusion line and the quantity of additive requested and obtaining the rpm from the graph "Flow dispensed = f (rotation speed) "related to the pump, saved in the MC-PLC board.

While the system operates, any differences between the theoretic quantity of additive and that really dispensed are compensated by increasing or reducing the rotation speed of the pump.

The use of the serial line RS485, suitable for managing a network, enabled the 3 lines to be centralized in one single operator panel.

The MC-PLC board, thanks to its numerous peripheral points and its large memory, is able to economically resolve many problems which would be difficult to resolve with other systems.