Hach 900 MAX - Manual (Page 63)

Page 61
8990sensors.fm Sensor Setup
Section 4 Sensor Setup
4.1 Downlook Ultrasonic Sensor
4.1.1 Downlook Ultrasonic Sensor Connection
The downlook ultrasonic sensor connection is located on the back side of the
refrigerated cabinet. The gray rectangular box houses the ultrasonic module
and the transducer connector labeled ULTRASONIC. The connector is keyed
and can only be inserted in the proper orientation (key up).
4.1.2 Downlook Ultrasonic Sensor Programming
The downlook ultrasonic sensor does not require specific programming,
unless more than one sensor option is connected to the sampler. When more
than one sensor option is connected to the sampler:
1. From the Main Menu, select OPTIONS>LEVEL SENSOR.
2. Select Ultra-Sonic using the CHANGE CHOICE key. Press ACCEPT .
4.1.3 Downlook Ultrasonic Sensor Calibration
Calibrate the current water level via one of two methods; Liquid Depth or
Sensor Height. An Invisible Range can also be set which allows the
transducer to ignore reflections from obstructions between the sensor and the
water surface, such as ladder rungs, channel side walls, etc. Each method
has its own advantages and disadvantages; selecting the proper method will
depend upon the site conditions. Calibrate the ultrasonic sensor each time the
sensor is installed at a new site.
4.1.3.1 Liquid Depth
This method requires the level or depth of liquid in the channel that is
contributing to flow. In a round pipe, the entire depth typically contributes to
flow. In a weir, only the depth that is flow over the weir plate contributes to
flow. Level Depth calibration is primarily used when:
• Access is available to the primary device for a physical measurement of
the liquid depth, and
• When water is flowing during installation (channel is not dry).
Note: Always re-check the
Level Adjust when re-installing the
flow meter. 1. From the Main Menu, select OPTIONS>ADVANCED
OPTIONS>CALIBRATION>ULTRASONIC SENSOR.
2. Select Calibrate U-Sonic using the UP and DOWN keys. Press SELECT .
3. Select Standard as the type of Ultrasonic Transducer using the CHANGE
CHOICE key. Press ACCEPT to continue.
Temperature Time Constant
The speed of sound in air varies with the temperature of the air. The ultrasonic
sensor is equipped with temperature compensation to help eliminate the
effect of temperature variation under normal site conditions. The transducer
must be equal to the ambient air temperature at the site prior to calibration for
optimum results. The manufacturer recommends that sensors be shielded
from direct sunlight for this reason.