User manual

Chapter 1 Introduction
5
20 Gear Drive, Plymouth Ind. Park, Terryville, CT 06786
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This chapter serves as an introduction to the 1761H module. It highlights potential
applications, compatible transducers, and all of the modules’ features, including
those added since the last revision.
Overview
The 1761H module is the Allen Bradley 1771 I/O
compliant card that converts resolver signals to digital multi-
turn position and tachometer data that can be reported over
the backplane using either block or single transfers. This
module eliminates the separate resolver decoder box, PLC
input card, and associated wiring needed to bring the digital
data into a PLC.
Like an absolute optical encoder, a resolver is a single
turn absolute sensor that converts an angle into electrical
signals. However, this is where the similarities end. The
resolver is an analog device that does not contain sensitive
components such as optics and electronics that may be
damaged by severe environmental conditions. Also, the
position resolution of a resolver is limited only by the
electronics that decode its signals. The module can produce
an absolute 20 bit multi-turn position value with a maximum
12 bits (4,096 counts) per turn when an AMCI transducer is
connected to it.
The transducer that connects to the 1761H contains two
resolvers. These resolvers are geared together in a vernier
arrangement. The module decodes the separate resolvers and
combines their positions into an absolute multi-turn position.
The 1761H accepts a single dual-resolver transducer.
A 1761H application generally falls into one of two categories.
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Rotary Application -
The resolver position directly correlates to an angular position on
the machine. One example is monitoring a rotary table by attaching a multi-turn monitor
and control such functions as motor braking to stop the table at its stations.
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Linear Application -
The resolver position correlates to a physical length. One example
is a packaging machine where the transducer completes multiple turns for each product.
Here the transducer position is used to control when glue is applied or when the package
is cut to length. Another example of a multi-turn application is monitoring the position
of a load on either a track or ball screw such as a press shut height monitor. In this type
of application, linear position is translated to rotary position through either a wheel or
gearing. The transducer completes several rotations in order to travel the complete
distance.
AMCI also has a line of cable reel transducers for use in some linear applications. A
cable reel transducer has a stranded stainless steel cable wrapped around a spring
loaded drum. As the cable is pulled out of the transducer, the drum rotates, which in
turn rotates the internal resolvers. The cable is retracted by the force of the drums'
spring. Distances of up to forty-five feet can be measured with these transducers.
Figure 1.1 1761H Module