Xylem H-3342 - Manual (Page 6)

1-2 Introduction
H-3342
1.1 Operation
The H-3342 is a precision shaft encoder with a resolution of 65,536 counts per revolution
(.000015 feet with 1.0 ft circumference pulley). Internally the H-3342 has two non-contact
encoders mounted on the same shaft. An optical encoder measures the shaft angle and a
magnetic turns counter counts the number of revolutions. The optical rotary position sensor
measures the shaft angle within a 360° range. As opposed to incremental encoders, the optical
encoder measures the absolute position rather than the change in position. Internally, an infrared
LED flashes through a circular bar code onto a linear array sensor. A microcontroller decodes
the image into a unique position. Due to manufacturing tolerances of the bar code, the accuracy is
less than the resolution; 4096 counts per revolution (.00024 feet with 1.0 ft circumference
pulley). The turn counter monitors complete revolutions of the shaft and can count up to
±32,768 revolutions. Together the encoders provide an “absolute” measurement. The shaft
position will not be lost if the power is removed, even if the shaft rotates while the power is off.
During normal operation, the SDI-12 data recorder sends an address together with a command to
the H-3342. The H-3342 wakes up from its low power sleep mode, converts the shaft position
into feet, meters or other units and stores this data in its data buffer. Once the data is ready, the
data recorder collects the data from the H-3342's data buffer.
1.2 LCD Display
The H-3342 has a 4-1/2 digit LCD display which shows the last measured value. The display
uses negligible power and is always visible. The display will show either ±199.99 or ±19999
digits depending on how the H-3342 is configured.
1.3 “Read” Button
When pressed, the ‘Read’ button causes the H-3342 to continuously make measurements and
update the display. The “±” sign flashes while making measurements indicating the display is
being updated even if the value is not changing. When the button is released the display will
hold the last measured value. Measurements initiated from an attached SDI-12 data logger will
also cause the display to update.
1.4 Using the Adjust Knob to Change the Stage
The offset adjustment is a rotary digital encoder which is accessed by removing the attached dust
cover. The encoder has a slot and is easily rotated with a screwdriver or other flat blade tool.
Replace the dust cap whenever the adjustment is not being used.
While the ‘Read’ button is pressed, the Adjust screw may be turned to increase or decrease the
current Stage reading. Turn the adjustment screw clock-wise to increase the Stage and counter-
clock wise to decrease the Stage. Turning the adjust screw slowly will change the hundredths
digit while turning the screw fast changes the tenths digit. This allows one control to make both
fine and course adjustments.