AquaCalc Support has received complaints of the AquaCalc not counting. In each complaint we found that the reset problem was caused by improperly maintained or adjusted equipment feeding inconsistent signals to the AquaCalc. These are the exact types of problems the update revisions were designed to catch. Unfortunately, due to the design of the Pymy current meter and the precision needed to adjust the whisker hair, more complaints have involved Pygmy current meters than other types.
The AquaCalc and its operating system firmware were designed not miss a click or double count a click. This makes the AquaCalc robust in its ability to count signals generated by various current meters. These signals are commonly called “clicks” when heard through headphones.
During counting, the AquaCalc looks for patterns in the clicks and determines a “window” of time in which it expects the next click to appear. When the AquaCalc senses a click that it believes is not a valid signal (most often a click that has occurred outside the “window”: too soon before or too long after the previous click), it warns the user and then “resets” the measurement time and counter to zero and begins counting again.
The “reset” function of the AquaCalc was originally designed to sense turbulent flow conditions in surging streams (which the USGS qualifies as a poor measurement) and inform the user. The AquaCalc recognizes a bad, missing or rejected signal and then to allow the user to take corrective actions to insure a quality measurement.
There are varying conditions that can cause an AquaCalc to reset during a measurement:
Any one of the above conditions will cause the AquaCalc to reset during a measurement.
Note: There is a small probability that the above problems can produce multiple clicks per revolution. If these false clicks are spaced at regular intervals in time, the AquaCalc could very well count them for the full 40 seconds and yield an erroneous velocity measurement.
Are you measuring in turbulent flow? Then the AquaCalc is doing its job correctly. Either select a different location, or use the “Halt” function to shorten the measurement time. Or enter an estimated velocity.
It was often found that poorly adjusted or maintained measurement equipment was the problem. (In fact, often technicians using the same equipment with head-sets were also getting false counts, but not realizing it.)
Given the greater difficulty in properly adjusting the cat whisker type Pygmy current meter, these points are more particular to the Pygmy meter than the Price AA but can affect both. We recommend the magnetic head for both models.
The cam and cat whisker contacts must be cleaned daily before or after usage. Oil and carbon build-up on the whisker and cam lobe increases the resistance in the electrical circuit, causing a week signal that the AquaCalc will reject. This rejection of signal was built into the AquaCalc to filter out false signals generated by the wading rod and terminal connectors on the sounding cable when submerged in highly conductive water. The wading rod and current meter acts as a capacitor and, depending upon the conductivity of the water, the signal strength can vary greatly.
The USGS has published standards for maintenance for current meters. in OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM NO. 99.06 available from the USGS website. You may also download an Adobe Acrobat (pdf) file that discusses meter mantanence in detail.
If you are using a USGS style magnetic head on your current meter, check the reed switch. As the reed switch ages, the reed switch spring will experience metal fatigue and eventually fail. As it is doing so it will be unreliable. Try replacing your reed switch.
Pygmy cat whisker meter spin test
An incorrectly adjusted Pygmy meter whisker can lead to the rapid buildup of carbon deposits in the contact chamber, degrading the electrical signal. We has found that a spin test of 60 seconds +/- 5 seconds will provide the correct amount of tension between the whisker and the cam lobe to generate a strong enough signal for the AquaCalc.
Spin test times less than those recommended above will work, but over time they increase carbon deposits on the whisker and cam lobe, thereby increasing the electrical resistance in decreasing the signal strength.
The increased tension on the cat whisker keeps the contact cleaner for longer periods of time by burnishing the cam lobe and whisker hair against each other. Slow velocities (2 to 3 counts in 40 seconds) with a large dwell angle of contact between the cat whisker and the cam, cause arching for longer periods, and tend to cause the build up of carbon faster than during normal velocities.
All electrical contacts should be inspected and cleaned on a routine basis. Areas that have been known to fail are:
A badly worn upper bushing will allow the bucket wheel assembly to wobble. If the cam lobe wobbles when in contact with the cat whisker, the AquaCalc could detect multiple clicks and reset.
A bad pivot pin can allow the bucket wheel to move vertically up and down producing false counts, which will cause the AquaCalc to reject the signal and reset the measurement.
If you continue to have reset difficulties after adjusting your equipment, please contact Customer Support.
I
We have replacement parts and cables for the AquaCalc line of stream flow computers including the Digital Pygmy Magnetic Head retro fit your old Pygmy Current Meter with a new digital magnetic sensor.