Stage Potentiometer

To: "E  - All WRD Employees"<distribution@usgs.gov>
Subject: Stage Potentiometer
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Date: Thu, 01 Feb 1996 11:14:22 -0600
From: "Dorothy E Greenwood, Secretary (Steno), Bay St. Louis, MS" <degreenw@usgs.gov>

                                             February 1, 1996

Memorandum

To:      All WRD Employees

From:    Acting Chief, Hydrologic Instrumentation Facility

Subject: EQUIPMENT AND SUPPLIES---Stage Potentiometer

The Hydrologic Instrumentation Facility (HIF) was recently made
aware of potential problems with the use of the Stage Potentiometer,
HIF stock number 5207010, for the collection of primary stage data at
continuous gaging stations.

The Stage Potentiometer, commonly called a Stage Pot, was designed 
as a stage sensor for non-critical applications with moderate accuracy,
where low cost is an important factor.  These pots are precision units
with a resistance tolerance of +/- 3% and a linearity of +/-0.1%.
With the proper data logger or Data Collection Platform (DCP) setup,
and proper wiring and measurement techniques, errors of +/-0.05 ft
are common.  THE STAGE POT DOES NOT MEET THE ACCURACY REQUIREMENTS
OF STAGE SENSING FOR PRIMARY RECORDS.

Stage Pots are intended for applications where continuous float
motion or "painting" does not occur. Continuous movement of the water 
surface, particularly at the same gage height, can cause wear of the 
internal contacts of the pot, resulting in intermittent contacts and
unreliable data.

Users should be aware of these limitations if they plan to use a 
stage potentiometer in their data collection network. If you have 
any questions concerning the use of the Stage Pot, please contact 
the HIF at (800)382-0634.


                                      /s/ Frank S. Henry