Wiring the MDC Boxes to the Machine Outputs


Wiring into the machine signals should only be carried out by a competent machine electrical engineer - never attempt to make live connections with the machine powered on. If the machine is still under warranty and you have to modify any connections in the machine you will have to get the machine tool company's permission and confirm that it does not void the warranty. In these instances it is often easier to ask the machine tool company or an authorised engineer to fit the MDC box.

The MDC box can accept 5 to 50V DC signals or 110V AC signals and will convert these to an RS-232 level output. In practise nearly all signals are 24V DC or 110V AC (older machines). You do not need to use relays for the 110V AC signals - just wire them directly into the box.

Make the connections to the green connector and then push the connector firmly into the MDC box before powering up the machine.

To monitor the machine's status the MDC boxes should be wired into the machine's output signals.

1+ and 1- are normally connected across the machines 24V running lamp 2+ and 2- are normally connected across either the machines M02 (Program End) lamp, or across any 24V signal that operates once a cycle and indicates the end of a cycle (part counter, parts catcher, Colet open, parts conveyer etc). Because these signals are not always available it is often necessary to wire into the machine in other places, or to use the third input (3+ and 3-) to get a third signal for additional information about the machine state.

Ideally you would get the relevant connector signals from the machine tool builder or the machine's electrical schematic. If this is not possible then examine the machine while it is running to see which lights go on or off at the start and end of the cycle.

If you cannot find a light then it is often necessary to look at the I/O modules in the machine cabinet while it is running to spot suitable signals.

As a last resort you may have to check signal levels when the machine is running live. Always use an Oscilloscope, NOT a multimeter for this purpose as a multimeter only has about a 1K resistance - an oscilloscope normally has one MegaOhm. USB based oscilloscopes are readily available for under 100 Euros for laptops. You may have to get a Certificate of Live Working to prove you are qualified to do this before you are allowed to run the machine like this. Make sure you follow all relevant Health & Safety procedures (these vary according to country).

In the case of most milling machines, and a lot of lathes the easiest place to monitor the machine is directly across the light on the 'Cycle Start' light for the cycle start signal, and across the M30/M02 lamp (this can involve soldering across pins on the switch panel circuit board) for the part complete. If a bar feed is being used then look for a part catcher or part conveyor signal (often this is only accessible in the hydraulics panel of the machine) or a hardware parts counter. Other signals such as pallet positioning switches, chuck open signals, or bar feeder request signals have also been used. It is sometimes easier to use software monitoring (see separate section) to use a DPRNT statement at the end of each component.

It is often necessary to wire the monitoring boxes into the pilot lamps on top of the machine, these are normally a green, amber (sometimes blue) and red lamp in a wand or beacon on top of the machine. If these are fitted and their connections can easily be found in the control cabinet they are often the easiest way to monitor the machines state.

In some cases the lamp signals flash to indicate a paused state (waiting for operator) on the machine. This can be picked up in the DNC-Max settings to give an extra message (see Configuring Messages in DNC-Max for setting up messages).