Rockwell Automation SA500 AC Power Modules - Manual (Page 27)

Power Module Electrical Description 3-3
The PMI produces a nominal 26 volt rms 2381 Hertz sine wave reference output
signal which is capable of driving a 500 ohm load. The stator signals (sine and cosine)
are input through a matched isolation transformer pair. The transformers are matched
for gain and phase shift. The ratio of the sine and cosine amplitudes is then converted
to an angular position. Position data is sent to the UDC module by the PMI before
every scan of the UDC task. The UDC task calculates speed using this position data.
The PMI supports two methods of sampling the digital position of the resolver,
time-driven and event-driven. Both methods may be used simultaneously. In the first
method, the position is sampled once per UDC task scan at the rate defined in the
SCAN_LOOP control block in the UDC task. This block tells the UDC task how often
to run based on the CCLK signal on the AutoMax rack backplane. The PMI sends the
position data to the UDC module immediately before it is needed by the UDC module
for the next UDC task scan. Position data measured using this method is stored in the
UDC module's dual port register 215/1215 in the format shown in figure 3.1 or 3.2.
The second method allows position sampling between scans or when an external
event occurs by using an external strobe. The resolver interface includes an isolated
24 volt DC input with a relatively high degree of filtering (approximately 800 Hz). The
external strobe input circuit is shown in figure 3.3.
Figure 3.4 shows the relationship between the time the external strobe is detected and
the point at which the resolver position is sampled. Response time is subject to
temperature, component tolerance, and input voltage level. Note that the input signal
pulse width should be greater than 300 µsec and the frequency should be less than
1000 pulses per second.
Figure 3.2 – Resolver Data Format (14-Bit Mode)
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
bits
revolution counter
resolver data
Figure 3.3 – External Strobe Input Circuit
+
-
EXTERNAL
STROBE
INPUT
300
300
.33µF
2.55K
1.24K
5K
Vcc
681K 10K
TO
MICRO-
PROCESSOR
14K
.01µF
681K
475K