1 Introduction
The basic encoding device is an incremental optical encoder, which transforms the rotating mechanical
input to a quadrature type of electrical output signal. This signal is brought out of the enclosure through a
4-conductor cable which is retained by a weather-tight cable clamp. Connections to the cable wires are
easily made to the screw-clamped type of barrier strips on the Loggers, using only a flat-bladed
screwdriver. Other receiving instruments may be used, if their inputs can be scaled to the Encoder output.
The Type A/F Encoder generates a “quadrature” signal, which means there are four (4) states that this
device can be in. Transitions from one state to the next is well defined so that the pulses can be
translated into rotation movement.
1.2 SAFETY INFORMATION
Before performing any procedure in this manual, read all applicable warnings and cautions.
1.3 FLOAT WELLS AND INSTRUMENT SHELTERS
Information on suitable float wells and instrument shelters can be found in the Stevens Water Resources
Data Book, any edition.
1.4 TYPE A/F ENCODER SPECIFICATIONS
Input, Standalone
: Shaft, supported by ball bearings and threaded for Stevens float pulley clamping
hardware; the shaft drives the internally-mounted encoder; the pulley, float, float tape or line and
clamping hardware are optional.
Type A/F Encoder, basic
: Incremental optical disc and electronics assembly in sealed enclosure;
encoder input shaft is threaded onto recorder input shaft; float pulley load is not transferred to encoder.
Output
: Two 5 volt signals in quadrature, with 100 states (400 transitions) per input shaft revolution.
The output of a quadrature encoder is a two-bit gray code, specifically it has the sequence 00 01 11 10
00.
More specifically, if the output is 00 and it goes to 01, you know that the encoder has moved one “tick”
clockwise. If it is 00 and goes to 10 then you know it moved one tick counter clockwise. If it goes from 00
to 11 you know you missed an intermediate tick. It can be useful to flag this case so that you know your
input isn’t accurate, but generally it is safe to ignore it as if the knob didn’t move.
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