Care and Calibration of Recording Instruments

Abstract

RECORDS of a filtration plant are very important as they are open to public inspection and may have to be produced in court when necessity demands. This is particularly true of public utilities, which are required by law to publish annual reports not only of their finances but of their operation as well. Most plants are equipped with enough meters and gages to enable them to check the results and by a process of elimination find the meter or sets of meters that are in error. For instance, Milwaukee meters its raw, wash and filtered water, and takes elevations of clear-water reservoirs and coagulation basins with continuously recording gages. By addition or subtraction, using the input and outtake method, it is possible to account for all the raw water pumped daily until it leaves the plant. This check holds for the water purification plant alone and is dependent on tight valves and absence of leakage. An additional continuous check of the quantity of water is provided by the high-lift stations, which take water from the clear wells and pump it into the distribution system. The accuracy of this check is also dependent on tunnel leakage from the plant to the pumping stations and on the permissible error in their meters. By applying these checks daily and recording and analyzing the results, slowly developing discrepancies can be discerned, and through a process of elimination the finger of suspicion can be pointed at the meters that need care and calibration, long, before any damage is done to the records or to the instruments. When there is an abrupt change, such as occurs if an instrument needs repair, the operator on shift usually picks up the failure immediately. The gradual deviations are, however, much harder to detect, but may nevertheless accumulate so that sizable errors are recorded unless