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Introduction to the RD750
13
Compatible Sensors (continued)
Single and Multi-Speed Resolvers
The most common resolver is known as a
single speed
resolver. It is manufactured in such a way that one
turn of the resolver’s shaft produces one sinusoidal cycle on the sine and cosine output windings.
Multi-speed
resolvers are wound with additional poles so that one rotation of the resolver’s shaft produces multiple sinu-
soidal cycles on the outputs. This is important in three ways in RD750 applications:
Z-Pulse Output:
The RD750 Encoder Output emulates the electrical cycles of the resolver. For exam-
ple, if a 5-speed resolver is used, the RD750 will output five Z-pulses for every mechanical rotation of
the resolver’s shaft.
Maximum Position Resolution:
The RD750 emulates the 20-750-ENC-1 option module in Rockwell
Automation software. The ENC-1 module has a resolution limit of 80,000 counts per turn. If this value
is exceeded, velocity data and motor commutation angle calculations will be incorrect.
Resolver Tracking Speed:
As explained in the following section, Resolver Tracking Speed is the
maximum rotational speed at which the resolver position can still be accurately decoded. This refers to
the rate at which the sinusoidal outputs change, which is the mechanical rotational rate of the resolver’s
shaft multiplied by the resolver’s speed. For example, a 5X speed resolver whose shaft is rotating at a
rate of 2,000 RPM will have an apparent rotational rate of 10,000 RPM (2,000 RPM x 5).
Resolver Tracking Speed
Resolver Tracking Speed is the maximum rotational speed at which the resolver position can still be accu-
rately decoded. Exceeding these speeds can affect positional accuracy. Resolver Tracking Speed is based on
the operating frequency and desired position resolution.
: Maximum operating frequency for 16 bit resolution is 10 kHz
: Maximum operating frequency for 14 bit resolution is 12 kHz
: Maximum operating frequency for 12 and 10 bit resolutions is 20 kHz
Table 2 Resolver Tracking Speeds
A resolver tracking error may be reported by the RD750 during times of apparent extremely high accelera-
tion. The error is rare, non-fatal, and will clear itself once the acceleration rate decreases. The Resolver
Tracking Speed refers to the rate at which the sinusoidal outputs are changing. For single speed resolvers,
this is equal to the rotational rate of the resolver’s shaft. For multi-speed resolvers, this is equal to the rota-
tional rate of the resolver’s shaft multiplied by the speed of the resolver.
Operating
Frequency
Position
Resolution
Resolver Tracking Speed
(Single speed resolver)
2.0 to 2.5 kHz
OR
16 bit
7,500 RPM
3.0 to 5.0 kHz
OR
14 bit
30,000 RPM
6.0 to 8.0 kHz
OR
12 bit
60,000 RPM
10.0 to 20.0 kHz
OR
10 bit
150,000 RPM
