This is not a true calibration. The EIT 960 can not be field calibrated. Calibration must be done at the factory. A later model can be field calibrated.
When laymen speak of calibrating the EIT 960, they mean setting wier width and DIST at ZERO for the given application so that the output of the LED display is correct for the application. In addition to the weir width and distance at Zero there are other settings usually made at the factory which may need adjustment at the site as covered in the manual. Once set nothing should need changed because the circuits are digital and battery protected so that values should not drift. Once a year or as desired, check the equipment by one of the methods below. To meet your requirement for annual calibration.
If any problem occurs it is likely to be in the COEFFicient of TEMPerature circuit. Press "R" many times to display COEFF TEMP and other parameters. If Coefficient of Temp fails, the chart will show flow when there is no flow and the Coeff Temp will read "0". Coeff of Temp will usually read 40 to 60 (57 is common in summer). To correct the problem, turn power off for a minute and then back on. This problem has occurred twice in one month, but a couple times per year is typical.
Xmit Power should never reach 10 (volts). XP is the voltage needed to get a good echo. A low number such as 2 to 4 means there is good alignment. At no flow, but with stilling basin full and barely running over, check Distance at Zero(DZ) and Echo Distance(ED). |DZ - ED| should be <.03. If water is perfectly still, then |DZ - ED| may be as small as zero.
I check the chart display everyday for agreement with the expected flow. If peaks have unusual size or shape it is due to a process upset; usually the lagoon has run dry. If final effluent volume seems normal check the 960 manual for troubleshooting.
Normal Annual "Calibration"
Now check the ECHO distance during simulated flow
using a bucket of water set below the sensor and compare the distance to
the target with the value reported by the meter. If in error, factory work
is required. This is the method used by professional calibrators.
A Stronger Annual "Calibration"
1. Place a 7 or 8-inch concrete block below the sensor in the water
of the stilling pool. Lay a sheet of heavy metal on top of the block. Heavy
metal and smooth block provide a target that won't wobble.
2. Hold a meter stick vertically, parallel with the sensor axis, and measure the distance from the target to the bottom edge of the sensor (or the phi mark on old style sensors). Be careful that you do not press so hard against the target or sensor that you measure a disturbed distance. Record the measured distance to the nearest 1/3 millimeter (0.01 foot). Being careful not to disturb the target or sensor, read and record the Echo Distance observed on the EIT 960 display. Repeat the ruler and meter measurements 3 times. EIT claims agreement to 0.01 foot is possible in the laboratory and 0.02 foot is an attainable field comparison.
3. For greater confidence, take another set of measurements by changing the distance between the target and the sensor. I insert a 1 inch thick flat concrete block between the big concrete block and and the heavy metal target. I then repeat the measurement by using the meterstick and and recording the value observed on the 960 display. By using a seven-inch concrete block plus a 1.5 inch concrete block, I am able to simulate a normal flow almost exactly.
This is a report on my use of this flowmeter. I hope you find it helpful. Before December, I expect to install here a copy of the report form I am using.