Apparatus for recording pressure conditions in bore holes

Claim 1

MEASURING APPARATUS COMPRISING: A DIFFERENTIAL TRANSFORMER HAVING RELATIVELY MOVABLE PRIMARY AND SECONDARY ELEMENTS; MEANS FOR EXCITING SAID PRIMARY ELEMENTS; PHASE SENSITIVE DETECTING MEANS HAVING CONNECTIONS RECEIVING INPUTS FROM SAID SECONDARY ELEMENT AND FROM SAID MEANS FOR EXCITING SAID PRIMARY ELEMENT AND PROVIDING AN OUTPUT REVERSIBLE IN RESPONSE TO PASSAGE OF SAID PRIMARY AND SECONDARY ELEMENTS THROUGH A RELATIVE NULL POSITION; A REVERSIBLE MOTOR; MEANS INDICATING THE OPERATION OF SAID MOTOR; SENSING MEANS CONNECTED TO ONE OF THE ELEMENTS OF SAID DIFFERENTIAL TRANSFORMER TO DISPLACE SAID ELEMENT IN ACCORDANCE WITH CHANGES OF A VARIABLE SENSED BY SAID SENSING MEANS; MEANS CONNECTING SAID MOTOR TO THE OTHER OF SAID ELEMENTS OF THE DIFFERENTIAL TRANSFORMER TO EFFECT DRIVE OF THAT ELEMENT BY THE MOTOR; SWITCHING MEANS CONNECTED TO BE OPERATED BY THE ELEMENTS OF SAID DIFFERENTIAL TRANSFORMER TO BE SWITCHED TO A FIRST CONDITION IN RESPONSE TO DEVIATION OF SAID ELEMENTS FROM NULL IN EXCESS OF A PREDERERMINED DEVIATION IN ONE DIRECTION OF RELATIVE MOVEMENT OF SAID ELEMENTS AND TO BE SWITCHED TO A SECOND CONDITION IN RESPONSE TO DEVIATION OF SAID ELEMENTS FROM NULL IN EXCESS OF A PREDETERMINED DEVIATION IN THE OTHER DIRECTION OF RELATIVE MOVEMENT OF SAID ELEMENTS; AND CONTROL MEANS CONNECTED TO DELIVER POWER TO OPERATE SAID MOTOR REVERSIBLY, SAID CONTROL MEANS RECEIVING THE OUTPUT OF SAID PHASE SENSITIVE DETECTING MEANS AND NORMALLY MAINTAINING SAID MOTOR INACTIVE, BUT RESPONSIVE TO EITHER OF SAID FIRST AND SECOND CONDITIONS OF SAID SWITCHING MEANS TO INITIATE OPERATION OF THE MOTOR TO DRIVE TH MOTOR-DRIVEN ELEMENT OF SAID DIFFFERENTIALK TRANSFORMER TO A NULL POSITION WITH RESPECT TO THE OTHER OF SAID ELEMENTS.