Delta RMC151 - Manual (Page 82)

RMC70/150 and RMCTools User Manual
modules use 16-bit Analog-to-Digital converters. The RMC150 A module uses 12-bit
Analog-to-Digital converters.
The effective resolution of the Analog-to-Digital converted signal is increased by the
following items:
1. Oversampling
The AA, A2, AP2, H, and G analog-to-digital converters are read eight times
per sample, increasing the effective resolution of the Analog-to-Digital
converted signal. For example, the eight times oversampling causes a 16-
bit input's effective resolution to be 19 bits (one part in 524,288) over the
full ±10V range.
The Universal I/O module's analog inputs are sampled at 60kHz, which is a
minimum of 15 times oversampling.
2. Input Range Gain
Choosing the ±5V or 4-20mA ranges on the RMC150 H or G modules
changes the gain of the analog input, increasing the resolution over the
requested range.
Due to the factors listed above, the effective resolution of the RMC analog inputs is
as shown in the table below.
Module ±10V ±5V 4-20mA
AA, A2,
AP2
38.1µV 0 .15µA
Analog
(H)
38.1µV 19.1µV 0 .076µA
Analog
(G)
38.1µV 0 .15µA
Analog
(A)
610µV 305µV 1 .221µA
Universal
I/O
38.1µV 0 .15µA
Note:
Typically, noise on the analog signals will exceed these small resolution values, and
will have a larger impact on system performance.
• Quadrature
Quadrature encoder resolution is specified in pulses (also called lines) per revolution
on rotary encoders or pulses per inch (or meter) on linear encoders. The RMC
quadrature input will decode the pulses to generate four counts per pulse. So the
internal resolution on the RMC will be four times the resolution of the encoder given in
pulses. Encoders with 2000 pulses (or 8000 counts) per turn are common. The
maximum quadrature encoder frequency is limited to 8,000,000 counts per second for
the RMC70 and 4,000,000 counts per second for the RMC150.
Delta recommends that the quadrature Counts value should not exceed 24 bits
(16,777,216). See the Exceeding 24 Bits section below.
• Resolver
The RMC150 Resolver module can be configured for 14 or 16 bits per revolution. One
revolution of the resolver will always consist of 65,536 counts on the RMC, regardless
of the resolver resolution parameter. With 16-bit resolution, the counts will increment
by one; with 14-bit resolution the counts will increment by four.
Exceeding 24 Bits
The quadrature and SSI inputs can handle Counts values up to 32 bits. However, Delta
recommends that you design your system and programming such that the quadrature
and SSI Counts value do not exceed 24 bits (16,777,216). The RMC can still interface
62 Delta Computer Systems, Inc.