Campbell Scientific QD1 Incremental Shaft Encoder Interface - Manual (Page 7)

QD1 INCREMENTAL ENCODER INTERFACE
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TABLE 1. Datalogger Maximum and Minimum Range Limits and Storage Efficiency for Given
Output Resolution
Minimum Maximum Final Memory
Zero Magnitude Magnitude Locations/Data Pt.
Low Resolution 0.000 ±0.001 ±6999. 1
High Resolution 0.000 ±0.00001 ±99999. 2
The resolution of the low resolution format is
reduced to 3 significant digits when the first (left
most) digit is 7 or greater, as shown in Table 2.
TABLE 2. Format Range and Decimal
Location for Datalogger Low Resolution
Output
Range
(Absolute Value)
Decimal Location
0-6.999 X.XXX
7-69.99 XX.XX
70-699.9 XXX.X
700-6999. XXXX.
It may be necessary to use high resolution or an
offset to maintain the desired resolution. For
example, if water level is to be measured and
output to the nearest 0.01 ft., the level must be
less than 70 ft. for 0.01 ft. increments to be
maintained in low resolution. If the water level
is expected to range from 50 to 80 feet, the data
could either be output in high resolution or could
be offset by -20 ft., transforming the range to 30
to 60 ft. If the datalogger's storage capacity is
limiting, it is best to maintain the measurement
resolution with an offset and store the data in
the more memory efficient low resolution
format.
8. QD1 TIMING DIAGRAM
Figure 1 is a simplified timing diagram of the
pulses into and out of the QD1. In actual
operation, the 5 V supply to the encoder is
strobed which causes the encoder output (S1,
S2 QD1 inputs) to be strobed. S1 and S2
inputs are shown as full square waves in Figure
1 for ease of conception. The time between
transitions shown is the minimum 0.75 ms.