Abstract

A shaft position recorder apparatus and method are described which can be used for recording changes in liquid levels. The recorder employs an electronic memory for storing the changes in liquid levels which are entered into the memory at predetermined time intervals if they exceed a predetermined magnitude or "deadband". The recorder apparatus employs a shaft position encoder as an input means for supplying a group of pulses for each measured change in shaft position or liquid level so that the sequence of the pulses indicates whether the change was an increase or decrease from the previous reading. The preferred shaft encoder includes three reed switches which are operated by four permanent magnets mounted on a support disk which rotates in accordance with the position of the shaft, such shaft being coupled to a float pulley when used as a liquid level recorder. The reed switches are closed in different sequences when the support disk is rotated in opposite directions to produce the groups of pulses on three parallel outputs connected to a computer for analysis to determine if level change is up or down; and to produce a present level signal. The recorder contains a temporary or scratch pad memory which stores a datum reference signal corresponding to the previously measured liquid level signal. This datum reference signal is compared with the present level signal to produce a difference level signal corresponding to the differences in their amplitude which is then compared with a predetermined deadband limit signal to produce an output difference level signal when it exceeds such deadband. The output difference level singal is periodically gated every 15 minutes to a permanent memory where it is stored and is also transmitted to the datum memory to update the datum reference signal. In addition, the recorder includes a maximum level memory and minimum level memory which continuously monitor the present level signal, temporarily store and transmit maximum and minimum level signals through gates to the permanent memory at the end of a predetermined time period such as every 24 hours.