Portable display and control terminal for wells

Claim 1

A portable graphic display terminal for use with a well production control system having a first transducer for generating a signal representative of a load on a sucker-rod string and a second transducer for generating a signal representative of a position of said rod string, said terminal having means for monitoring well conditions and for supplying control parameters to said control system, said terminal comprising: a liquid crystal display module for displaying data from said control system; keyboard means for entering display command signals and system control signals into said terminal; means for connecting said terminal to said control system; a source of potential having first and second output terminals; and a temperature compensating circuit connected between said display module and said first output terminal for supplying an operating voltage to said display module which keeps the brightness contrast of said display module substantially constant over a range of operating temperatures, said temperature compensating circuit including: a plurality of diodes each having an anode and a cathode, means for connecting the anode of a first diode to said first output terminal of said source, means for serially connecting the diodes with the anode of each of the other diodes connected to the cathode of an adjacent diode, an electrical impedance connected between said second output terminal of said source and the cathode of a last of said diodes, and means for connecting said cathode of said last diode to said crystal display module.