Explanation of the criteria for classification and numbering of components      C71.3.01
(DEC 99)
Explanation of the dates on the component's description



1.   Purpose and objectives

     To measure fluid levels including levels of streams and lakes or in irrigation and sewage systems.

2.   Description

     The sensor is usually housed in a stilling well. The unit consists of float, counterweight, beaded chain, and shaft encoder.  As the float rises or falls with water level, the incremental change in level is 
sensed and a signal is sent to a nearby radio transmitter station where it is relayed to an automated data collection substation (see component F00.3.05). While the float sensor is passive, it is usually used in conjunction with a self-contained radio transmission station consisting of battery power pack, radio transmitter and antenna housed in a standpipe assembly (see component C30.3.01, "ALERT Precipitation Gauge"). Accuracy and resolution of 1 percent are attainable. A 30.5 cm pulley would give accuracy and resolution of .305 cm.

3.   Input

     Water level.

4.   Output

     Station identification and water level value for reception by component F00.3.05 "ALERT data collection substation".

5.   Operational requirements and restrictions

     Two people should be trained in the installation and maintenance of the sensor when it is used in conjunction with components C30.3.01 and F00.3.05; one or two days of training is necessary. The stilling well should be of a sufficient diameter to minimize internal wave action, and the float sensitivity properly selected to prevent a drain on the transmitter battery due to sending unnecessary signals.
     The battery may be recharged with solar cells or replaced annually or after 20,000 transmissions, whichever comes first. A relay tower with repeater may be necessary.

6.   Form of presentation

     Technical description of the sensor.
7.   Operational experience

     Has been used successfully worldwide, with the most extensive use in the U.S.A. Use has been particularly advantageous for basins where time to flood peak is less than 24 hours.

8.   Originator and technical support

     The technology was originally developed in cooperation with the Sacramento(USA)River Forecast Center, U.S. National Weather Service.
     A list of vendors providing technical support can be obtained from links on the home page of the ALERT Users Group.  The address of this home page is currently:

9.   Availability

     From the HOMS National Reference Centre for U.S.A.

10.  Conditions on use

     Descriptive material available free. The sensor, which is for sale by commercial vendors, may be sold separately or in a package with the standpipe-transmitter station.


(First entered: 28 JUL 83

Last updated: JUL 99)