Product Alert #62
Water Level Instrument (6541A)
Manual Up / Down and Reset Button Errors
11 November 2002
Problem
The 6541A Precision Water Level Instrument may not always count by one digit when the up/down button is pressed. On occasion reset may not synchronize the display and Logger level to zero. The failures fall into three categories:
- The up/down switch results in an increment of 2-4 on the screen.
- The up/down button results in a large increase (100+) on the screen.
- The reset results in a difference between display and Logger level of 1-10 units.
Correction
The first failure is random in nature and is induced by infrequent noise in the switch circuitry. This has been corrected in all units manufactured after May 2002, and with serial numbers greater than 001193.
The second failure is more problematic to recover from during commissioning, but has a simple fix. Gently tap the pulley or stainless steel cable connected to the float so as to move the encoder off the dither-point, which causes a run-away count when the manual button is depressed. This has been corrected in all units manufactured after November 2002, and with serial numbers greater than 001218.
The third failure is related to the second, and occurs when the unit is reset while the wheel is rotating, or at a dither-point. Hold the wheel stationary with a finger, while resetting the unit to correct for this. This has been corrected in all units manufactured after November 2002, and with serial numbers greater than 001218.
It is advisable for units with serial numbers less than 001218 to always confirm that the display and logger level readings agree during commissioning and on subsequent visits. If the two readings are different, follow the fix for the third failure to correct the mis-match, then reinstate the level reading using the up/down buttons.
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