Delta MMC120 - Manual (Page 13)

MMC120 Linear Motion Control Module Description
Delta Computer Systems, Inc. 360/254-8688 13
DESCRIPTION
Principle Of Operation
Position Measurement
The MMC120 has interface circuitry for two magnetostrictive transducers. Each axis can be configured for a
Start/Stop transducer or a Pulse Width Modulated transducer by changing the axis' Configuration Word. To
make a measurement with a Start/Stop transducer, the MMC120 sends an interrogation pulse to the
transducer. The transducer responds by returning 2 pulses -- a 'Start' pulse and a 'Stop' pulse. The counters
on the MMC120 are active between the two pulses. The time between the pulses is proportional to the
transducer position.
Interrogation
Pulse
Start Pulse Stop Pulse
Counters Active
Start/Stop Pulse Transducer
To make a measurement with a Pulse Width Modulated transducer, the MMC120 sends an interrogation pulse
to the transducer. The transducer responds with a return signal that is high while the transducer is
determining its position. The counters on the MMC120 are active while the return signal is high. The width
of the return signal is proportional to the transducer position.
Interrogation
Pulse
Counters Active
Return Signal
Pulse Width Modulated Transducer
While the counters on the MMC120 are active, they count the number of half-cycles of a 60 MHz clock (120
MHz effective rate). At this frequency, each half-cycle represents less than 0.001 inch displacement of the
axis.
The MMC120 converts the Transducer Counts read from the counters to an ACTUAL POSITION in user-
defined Position Units (usually 0.001 inch) for use by the Quantum Programmable Controller.