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 detecting current through an initiator comprising:
 supplying current to the initiator, wherein the supplied current is less than the current necessary to initiate the initiator;   detecting whether current is flowing through the initiator; and   toggling a digital input of a switch corresponding to whether or not current is detected flowing through the initiator.   
     
     
         2 . The method of  claim 1 , further comprising initiating the initiator. 
     
     
         3 . The method of  claim 1 , further comprising determining whether or not an initiator is present. 
     
     
         4 . The method of  claim 1 , further comprising sending a signal to a surface location corresponding to the measured current. 
     
     
         5 . The method of  claim 1 , further comprising testing the initiator with a supplied current that is less than the no-fire current of the initiator. 
     
     
         6 . The method of  claim 1 , further comprising isolating the initiator from a power source. 
     
     
         7 . The method of  claim 1 , further comprising adjusting the supplied current based on the detected resistance of the initiator to optimize the accuracy of the current measurement. 
     
     
         8 . The method of  claim 1 , further comprising recording the detected current over time to monitor the integrity of the initiator during the perforating process. 
     
     
         9 . The method of  claim 1 , further comprising using an analog-to-digital converter (ADC) to measure the voltage across the initiator, thereby enabling calculation of the initiator's resistance. 
     
     
         10 . The method of  claim 1 , further comprising applying a high-impedance path in parallel with the initiator to ensure that the current flowing through the initiator remains below its no-fire threshold during detection. 
     
     
         11 . The method of  claim 1 , further comprising generating an alert if the current detected through the initiator falls outside a predetermined range, indicating a potential fault in the initiator or wiring. 
     
     
         12 . An apparatus for detecting current through an initiator comprising:
 An initiator in series with a high-impedance resistive divider, the high impedance resistive divider further comprising a plurality of resistors in series that are in parallel with a low side initiator voltage isolation switching device, wherein the initiator voltage isolation switching device allows a small amount of electrical current to flow through the initiator and the resistive divider can toggle a digital input of the switch's MCU between high (on) or low (off) depending on the current detection device detecting current passing through the initiator.   
     
     
         13 . The apparatus of  claim 12  wherein the value for the plurality of resistors sum to 9.9 MΩ. 
     
     
         14 . The apparatus of  claim 12  wherein initiator current is 50 μA at 500 volts. 
     
     
         15 . The apparatus of  claim 12  further comprising a clamping Zener diode coupled to the initiator, wherein the clamping Zener diode provides high voltage protection to the current detection device. 
     
     
         16 . The apparatus of  claim 12  further comprising a rectifier diode directing current into a voltage rail, wherein the rectifier diode provides high voltage protection to the current detection device. 
     
     
         17 . The apparatus of  claim 12  further comprising a means for providing high voltage protection to the current detection device. 
     
     
         18 . The apparatus of  claim 12  further comprising an electrically shunt coupled to the initiator voltage isolation switching device. 
     
     
         19 . The apparatus of  claim 18 , wherein the shunting is accomplished using a depletion-mode MOSFETs turned on and off by a microcontroller. 
     
     
         20 . The apparatus of  claim 12  further comprising a microcontroller supplied with power from a wellsite.