Product Alert #60B
Water Level Instrument (6541A)
Spontaneous Level change and Battery Life
22 June 2003
Problem
The 6541A Precision Water Level Instrument, with serial numbers in the range 00946 – 01159, may report spontaneous level errors (often at high ambient temperatures). In addition, manual switches may increment the display by more than one digit when pressed (refer to Product Alert #62 for additional information).
The error is due to temperature effects on new release HP Optical Encoder (wheel rotation transducer) fitted in the 6541A Precision Water Level Instruments with serial numbers 00946 – 01159, and shipped during August – May 2002. The error is more noticeable if the ambient temperature is above 35° C.
6541A Precision Water Level Instruments, with serial numbers in the range 01160 – 01259, and shipped during May – December 2002 have been modified to allow additional settling time. These units will exhibit a 50% reduction in the expected battery-life to 6 months (10AHr battery packs).
All units manufactured and shipped after January 2003, and with serial numbers greater than 01259, have the spontaneous level change and battery life problem fixed. Expected battery-life on all new units remains in excess of 12 months.
Correction
Product manufactured between May and December 2002 has addressed the requirements for new release HP Optical Encoders, at the expense of power consumption. The resulting power requirement is 1.8mA average, and 6 months operation on a Unidata Model 6910A 10Ahr STARLOGGER Battery Pack (shipped with 6541-X1 instruments).
Customers who experience inexplicable instability, or spontaneous level changes (usually at elevated ambient temperatures) and whose serial numbers fall in the range 00946 – 01159, will need to return the instrument for modification.
Please Note
- This upgrade is only required if the 6541A Precision Water Level Instrument displays inexplicable instability, and will probably have a serial number in the range 00946 – 01159.
- Most instruments within the serial numbers 00946 – 01159 have already had the modification applied after manufacture, and can be reliably used.
- All instruments within the serial numbers 00946 – 01259 will have reduced battery life performance and should have their battery pack replaced every 6 months or earlier.
- All instruments with serial numbers greater than 01260 have stable level recording, and at least 12 months battery life.
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