Delta RMC151 - Manual (Page 208)

RMC70/150 and RMCTools User Manual
Pulse Width Modulated Transducer
The value obtained from the PWM or Start/Stop counter is put in the Raw Counts register
for that axis. The Raw Counts are converted to Counts and then into an Actual Position in
user-defined units.
Recirculations
Delta does not recommend using recirculations on MDT transducers. Recirculations have
historically been used to gain more accuracy in the measurement. However, with faster
counters on the controller, recirculations have become less important. In addition, the
highest accuracies are only available for MDT transudcers with SSI ouput, which don't
have any recirculation options.
Transducer Lengths
An MDT transducer takes a certain amount of time to determine its position. The time it
takes increases with position. Therefore, the length of the transducer dictates the
minimum Loop Time you can use.
The approximate formula for determining the maximum transducer length for a given
loop time is as follows:
Length(in.) = (LoopTime(ms) - 0.22)/0.0095
Using the formula, the following are maximum lengths for a given loop time. This
assumes no recirculations.
Loop Time Maximum MDT Transducer Length
500µs 29.4 inches
1000µs 82.1 inches
2000µs 187.3 inches
4000µs 397.9 inches
3.12.2. SSI Fundamentals
Synchronous Serial Interface (SSI) is a widely accepted controller interface. Position data from
the sensor is encoded in a binary or Gray Code format and transmitted over a high-speed
serial interface.
Important!
The RMC SSI inputs require RS-422 (5V differential) SSI inputs. They do not support single-
ended SSI inputs or higher voltage inputs.
SSI feedback is supported by the following modules:
 RMC70: MA axis module
188 Delta Computer Systems, Inc.