Electronic detection and control system

Claim 1

APPARATUS FOR PROVIDING SIGNALS INDICATIVE OF THE PHYSICAL EXTENT OF A FLOWABLE ELECTRICALLY-CONDUCTIVE MATERIAL SUCH AS A LIQUID, POWDER, GRANULAR AGGLOMERATE OR THE LIKE, COMPRISING: FIRST ELECTRICALLY-CONDUCTIVE MEANS, AND SECOND ELECTRICALLY-CONDUCTIVE MEANS SPACED FROM SAID FIRST ELECTRIVALLY-CONDUCTIVE MEANS; MEANS FOR CHANGING THE ACCUMULATION OF SAID FLOWABLE ELECTRICALLY-CONDUCTIVE MATERIAL ADJACENT SAID FIRST AND SECOND MEANS SO THAT SAID MATERIAL AT TIMES FAILS TO SAID FIRST AND SECOND MEANS AND AT OTHER TIMES FAILS TO BRIDGE SAID FIRST AND SECOND MEANS; A VACUUM TUBE HAVING AN ANODE, A CATHODE AND A CONTROL GRID AND CAPABLE OF BEING CONTROLLEDLY CHANGED PROGRESSIVELY AND CONTINUOUSLY BETWEEN A HIGH-CONDUCTION STATE AND A LOW-CONDUCTION STATE BY CORRESPONDING PROGRESSIVE AND CONTINUOUS VARIATION OF THE GRID-TO-CATHODE VOLTAGE THEREOF; RELAY MEANS COMPRISING A CONTROL COIL AND AT LEAST A PAIR OF CONTACTS HAVING AN OPENING AND A CLOSED CONDITION, SAID RELAY MEANS BEING RESPONSIVE TO INCREASES IN CURRENT THROUGH SAID COIL TO A PREDETERMINED FIRST RELATIVELY-HIGHER VALUE TO OPERATE SAID PAIR OF CONTACTS TO ONE OF SAID CONDITIONS AND RESPONSIVE TO DECREASES IN SAID CURRENT TO A PREDETERMINED RELATIVELY-LOWER SECOND VALVE TO OPERATE SAID PAIR OF CONTACTS TO THE OTHER OF SAID CONDITIONS; A SOURCE OF REFERENCE POTENTIAL; DIRECT-CURRENT CONDUCTIVE CIRCUIT MEANS CONNECTING SAID CONTROL COIL BETWEEN SAID CATHODE AND SAID SOURCE OF REFERENCE POTENTIAL; MEANS CONDUCTIVELY CONNECTING ONE OF SAID FIRST AND SECOND MEANS TO SAID SOURCE OF REFERENCE POTENTIAL AND THE OTHER OF SAID FIRST AND SECOND MEANS TO SAID GRID, WHEREBY THE POTENTIAL OF SAID GRID IS HELD SUB-