Multi-point calibration is used to improve the accuracy of a flow meter across its full rated flow rate range, resulting in a much flatter accuracy curve. Accuracy of a flow meter tends to lessen at lower flow rates however repeatability of the meter remains consistent. A meter might not be perfectly accurate at low flow rates, but it is inaccurate by the same amount each time. Multi-point calibration takes advantage of the steadfast repeatability of a Liquid Controls meter by identifying the amount of inaccuracy and correcting it with a linearizing algorithm during deliveries. In order to apply the linearizing algorithm, the degree of error for points along the accuracy curve must be identified by making a number of deliveries at different flow rates into a volumetric prover. Multi-point calibration is very beneficial for meter systems that experience a wide range of flow rates (for example, trucks that fill tanks of varying sizes) and for meter systems that have recently undergone maintenance or other alterations that could change the accuracy curve itself.
To begin the multi-point calibration process, ensure the Register is in the calibration mode by removing any existing seal wire and loosening the calibration bolt on the side of the register housing approx 5-6 turns. If a ticket printer is connected to the Register, make sure a ticket is in place and the printer is ready. If connected, the register will print a calibration ticket showing the current calibration as well as any existing multi-point calibration information of the register. If no ticket printer is connected or the calibration ticket is not desired, press the Abort key to skip the print process.
Before starting the process of multi-point calibration, ensure that the initial single point calibration has been completed and the meter is accurate and repeatable. All multi-point factors are based on this initial calibration.
Once in the calibration mode, select Calibration from the main menu to access the calibration screens. Scroll to Calibration screen 4/4 to access the multi-point calibration fields.
In the Calibration screen 4/4, notice the yellow key labeled Run Calibration. Press this key to begin the actual calibration process by performing the meter screen test and resetting the delivery volume to 000.000. At the same time, the Register will provide the permissive signal to the valve output to allow flow through the meter.
NOTE: All deliveries in the calibration mode have a resolution to the thousandths decimal place allowing for precise calibration. |
Begin to flow product into or through the proving device, ensuring that the metering system is delivering at the flow rate for the desired multi-point calibration point.
Once the desired multi-point calibration volume is reached, pressing the End button will return the Register to the Calibration menu screen 4/4. Navigate the selection bar to the Linearization Prover Quantity field, and press OK. Enter the exact volume to the greatest detail that was registered on the proving device, then press OK. The Register will automatically display a prompt to select which of the 16 available multi-point fields to perform the calibration. Next the Register will display a prompt to the flow rate of the previous delivery. Enter the flow rate that was used for the multi-point calibration that was just performed. At this point, the Register will calculate the percent of error between the prover and register for the multi-point and automatically add the % error amount. When complete, the screen will show the point on the screen–together with the flowrate and % error.
Repeat this process, ensuring that the calibration process is accurate, repeatable and within local Weights and Measures tolerance–or company regulations. Repeat this process for each of the different multi-point calibration flow rate points that are desired.
When setting up the linearization points, you can specify the maximum difference allowed between adjacent linearization points. While most metrological jurisdictions require a maximum of 0.25% error between adjacent flow rates, this value can be changed to a value within the range 0.00 - 1.00. This value is protected by the W&M seal on the register.
Follow these steps:
1.Select the Maximum Delta Linearization Error field and press the OK key.
2.Enter a value in the range [0.00, 1.00] and press the OK key.
NOTE: When sorted by flow rate, the delta error between two adjacent linearization points will be validated when the Linearization Mode field is set to Applied. |
Once all multi-point calibrations are complete, you must apply multi-point calibration. To do this, you must ensure that the difference between adjacent multi-point flow rate errors does not exceed +/- .25% or the Register will not allow you to apply multi-point. If all adjacent % error points are within this range, change the Linearization mode setting from Setup to Applied. If within tolerance, the field will remain at Applied. If out of tolerance, this field will toggle back to Setup and require additional low rate points to further improve the linear accuracy with the +/- .25% range.
Once all multipoint calibrations are made and linearization has been applied, tighten the calibration bolt on the side of the Register housing. If a ticket printer is connected and a final calibration ticket is desired, insert a ticket before exiting calibration mode and a ticket will print when prompted.