Addressable Switch with Initiator Detection and Initiator Resistance Measurement

Abstract

A method and apparatus for electrically detecting the presence of an initiator in a downhole tool by measuring the resistance of an initiator, electrically isolating the initiator from a power source, supplying current to the initiator less than the current necessary to initiate the initiator, detecting voltage through the initiator, and calculating the resistance of the initiator.

What is claimed: 
     
         1 . A method for measuring the resistance of an initiator comprising:
 electrically isolating the initiator from a power source;   supplying current to the initiator, wherein the supplied current is less than the current necessary to initiate the initiator;   detecting voltage through the initiator; and   calculating the resistance of the initiator.   
     
     
         2 . The method of  claim 1 , further comprising initiating the initiator. 
     
     
         3 . The method of  claim 1 , further comprising sending the measured voltage to a surface location. 
     
     
         4 . The method of  claim 1 , further comprising sending the calculated resistance of the initiator to a surface location. 
     
     
         5 . The method of  claim 1 , further comprising determining whether the initiator is functioning correctly using the calculated resistance of the initiator. 
     
     
         6 . The method of  claim 1 , further comprising determining whether the initiator is shorted using the calculated resistance of the initiator. 
     
     
         7 . The method of  claim 1 , further comprising determining whether the initiator is present using the calculated resistance of the initiator. 
     
     
         8 . The method of  claim 1 , further comprising testing the initiator using the calculated resistance of the initiator. 
     
     
         9 . An apparatus for measuring the resistance of an initiator in a perforating gun string comprising:
 an initiator coupled to a current limiter through a voltage isolation device;   a voltage isolation device which isolates the initiator from a power source; and   a voltage measurement device coupled to the initiator through a voltage isolation device wherein   the measured voltage is used to calculate the resistance of the initiator.   
     
     
         10 . The apparatus of  claim 9  further comprising a switch, wherein the switch is responsible for initiating the initiator. 
     
     
         11 . The apparatus of  claim 9 , the current limiter further comprising a resistor and a constant voltage source, wherein the resistor has a relatively large resistance compared to the initiator's resistance. 
     
     
         12 . The apparatus of  claim 9  wherein the voltage induced across the initiator is used to measure/calculate the resistance of the initiator. 
     
     
         13 . The apparatus of  claim 9 , wherein the calculated resistance of the initiator determines whether the initiator is functioning correctly. 
     
     
         14 . The apparatus of  claim 9 , wherein the calculated resistance of the initiator determines whether the initiator is shorted. 
     
     
         15 . The apparatus of  claim 9 , wherein the calculated resistance of the initiator determines whether the initiator is present. 
     
     
         16 . The apparatus of  claim 9 , wherein the calculated resistance of the initiator tests the initiator. 
     
     
         17 . The apparatus of  claim 10 , wherein the switch, upon receiving a signal from an operator at a surface location, measures the resistance of the initiator and transmits the measured resistance back to the operator. 
     
     
         18 . The apparatus of  claim 9 , wherein the supplied current to the initiator is less than the no-fire current of the initiator. 
     
     
         19 . The apparatus of  claim 17 , further comprising a resistor and a constant voltage source, wherein the resistor has a relatively large resistance compared to the initiator's resistance. 
     
     
         20 . The apparatus of  claim 19 , further comprising a microcontroller configured to automatically adjust the current supplied to the initiator based on the measured resistance to optimize the accuracy of the resistance calculation.