Campbell Scientific QD1 Incremental Shaft Encoder Interface - Manual (Page 5)

1
QD1 INCREMENTAL ENCODER INTERFACE
1. FUNCTION
The QD1 is designed as a general purpose
quadrature decoder to interface CSI's CR10,
21X, and CR7 dataloggers to incremental
encoders. This manual focuses on using the
QD1 with commercially available shaft encoders
used in water level applications (see Appendix).
If there are other incremental encoders of
interest, please contact CSI's Marketing
Department for support.
As the encoder rotates, it produces two square
waves which are 90` out of phase with each
other. When the rotation is reversed, the
relation of the two square waves is reversed.
The QD1 decodes the two square waves and
gates a voltage pulse to a datalogger pulse
counting channel (refer to Section 8). Two
pulse counting channels are required, one for
each direction of encoder rotation.
2. SPECIFICATIONS
Datalogger compatibility: CR10, 21X, CR7
Power supply: 4 to 5.6 V
Current drain: 0.2 to 0.4 mA avg.
Operating temperature: -25 to +50
°
C.
Humidity: 0 to 95%, noncondensing
Minimum time between input transitions:
0.75 ms***
Output pulse width: 0.25 ms @ 25
°
C
Signal magnitude, Volts: 0 (low), supply voltage
(high)
Dimensions (L x W x D, inches): 2.9 x 1.7 x 0.85
Weight (lbs.): 0.22
***NOTE: The minimum time between
input transitions implies a rate of 1333.3
counts/sec. To realize this specification,
the time between transitions must be evenly
spaced; a function of the encoder. A
diagram explaining "minimum time between
transitions" is given in Table 1, Section 8.
3. CONNECTIONS
Connections between the QD1 and the
datalogger are shown below. Connections from
the QD1 to two commercially available shaft
encoders are shown in the Appendix.
QD1
(datalogger side) DATALOGGER
+5 +5V (CR10) or
CAO (21X, CR7)
P1 PULSE CHANNEL
P2 PULSE CHANNEL
GRND G (CR10) or GRND
(21X, CR7)
NOTE: Datalogger pulse input channels
should be sequential for efficient datalogger
programming.
4. DATALOGGER PROGRAMMING
The program must measure the QD1 output
and process the "up" and "down" counts to
determine stage. For 21X and CR7
dataloggers, an additional step is required to
power the QD1 from a Continuous Analog
Output (CAO) channel. The following steps
outline the procedure. Notes on the various
steps are presented in following sub-sections.
An example program is given in the Appendix.
1. Load QD1 power supply level, 5000 mV,
into an input location (Instruction 30,
required for 21X and CR7 only)
2. Enable CAO to output QD1 supply voltage
(Instruction 21; required for 21X and CR7
only)
3. Measure QD1 up count and down count
output on 2 pulse count channels
(Instruction 3, 2 reps, high frequency
option)
4. Stage = up count + stage (Instruction 33)
5. Stage = stage - down count (Instruction 35)