US 4,546,442 AGranted

Microcomputer control system for desiccant dryer

AssigneePall Corporation

InventorCraig S. Tinker

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Abstract

A microcomputer-based programmable control system for desiccant air dryers monitors the level of moisture saturation of the desiccant beds and adjusts the regeneration cycle accordingly to optimize energy efficiency. The moisture sensors have capacitance probes and adjustable resistors as frequency determining components for precision oscillators. A multiple counter integrated circuit is controlled by the microcomputer to establish a predetermined time interval and to count cycles of the precision oscillators during the predetermined time interval to obtain final counts for each probe indicative of the level of moisture saturation in the respective desiccant beds. The microcomputer compares the final counts to predetermined threshold number in order to determine whether a regeneration cycle is required, and also compares the final counts to maximum and minimum threshold numbers to detect and indicate probe failure. A pair of high and low pressure sensitive switches is provided for each desiccant bed, and the microcomputer tests for coincidence of the high switches and the low switches to monitor full depressurization and repressurization of the regenerating bed and to analyze and indicate valve malfunction. The control system directly activates low current, low capacity solenoid valves which in turn operate high pressure pneumatic relays to drive the valves in the air dryer.

Claims7

Dependent claims

A control system for a desiccant gas dryer having a first desiccant bed and a second desiccant bed, gas to be dried being alternately directed by valves to pass through one of the beds providing adsorbtion of vapor while the other desiccant bed is being regenerated or is in an idle condition in response to at least one bed select signal and at least one regeneration enable signal, respectively, energy being required for the regeneration process, the control system comprising, in combination,

a capacitance probe in each desiccant bed so that the level of condensate saturation of the desiccant in each bed is indicated by the capacitance of the respective probe,
at least one oscillator having a frequency setting capacitance input connected to the probe in the desiccant bed having been used for adsorbtion of vapor, so that the oscillator frequency is indicative of the capacitance of the connected probe and thus indicative of whether the desiccant bed needs to be regenerated,
timer means for establishing a predetermined time interval,
means for counting the cycles of the oscillator frequency over said predetermined time interval,
means for obtaining a final count from the means for counting at the end of said predetermined time interval so that the numeric value of the final count is indicative of the level of condensate saturation of the respective desiccant bed, and
a microcomputer executing a stored sequence of instructions, said microcomputer comprising
first means for comparing the final count to a predetermined threshold count representative of the condensate saturation level for which regeneration is required, and
means for generating said regeneration enable signal in response to said means for comparing the final count to the predetermined threshold indicating that regeneration is required.

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Dependencies are inferred from the claim text.