OPEN CIRCUIT DETECTOR

Abstract: An open circuit detector for connecting devices in seismic data acquisition systems comprises two transformers (TM, TS), at least one signal source and at least one detection device. The detector is characterized in that the transformers' primary windings (W1M, W1S) are connected to the detection device(s) and the signal source to form a primary circuit for detection of impedance changes, especially those caused by an open circuit condition in the secondary circuit, and the transformers' secondary windings (W2M, W2S) are connected to the connecting device to form a secondary circuit or loop. A method for detection of an open circuit in a connecting device in seismic data acquisition systems by means of a detector comprising two transformers (TM, TS), at least one signal source and at least one detection device is characterized by connecting the transformers' primary windings to the detection device(s) and the test signal source to form a primary circuit, connecting the transformers' secondary windings to the connecting device to form a secondary circuit or loop, detecting impedance changes in the secondary circuit, and determining an open circuit condition based on said detected impedance changes.

Description: Open Circuit Detector The present invention is related to an open circuit detector and a method for detection of an open circuit in seismic data acquisition systems. In recording ground motion from reflected seismic waves by means of land seismic data acquisition systems it is often utilised high complexity electronic modules which are spread out in the terrain in a certain pattern. The distance between these modules is typically of some few hundred meters, and the units are normally connected to each other by multiwire cables, called "line cables". The line cables are divided in sections, and these are connected by means of connector interfaces. Geophones are connected together in small clusters called "geophone strings", which further are connected to the line cables via so-called "takeouts". In its simplest form, the takeouts are implemented as a connector between an array of passive geophones and the electronic modules for digitalisation of the seismic signals. In more advanced systems, the takeouts are implemented as active electronics and function as a node on a transmission system or a "sensor network". FigJ shows a typical component configuration of a "land seismic cable". The electronic modules on the end of the line cable sections can be digitalisation units that convert the seismic signals into digital format and interface these to a transmission or telemetry system. In more recent systems, the digitalisation is performed locally at each sensor or geophone, thus reducing the electronic modules to transmission links. The line cable between the electronic modules consists of several identical sections of typical 200 meters length. The electronic modules in all systems need power supply. This is achieved by means of dedicated power wires inside the line cable or superimposed on to transmission pairs as a 'phantom' coupling. Today's systems require a moderate power feeding scheme, implying usage of low enough voltages not to require compliancy with the 'Low Voltage Directive' (that is voltages under 60V for DC and under 48V for AC). In the future, systems will require more power and thus higher voltages for reducing power losses. Use of higher voltages leads to higher security requirements, such as assurance that no open connections exist in the system. As described before, the line cable sections are coupled by means of connectors. These connectors can be of male (pins) and/or female (socket) type. Connection between two female or two male elements is providedby adapters. Adapters are also used for splicing two connectors. The different combinations of couplings lead to a risk of having energised pins at the end of a line cable section. The object of the present invention is to avoid such energised open connections. This object is achieved by means of a sensing element or system that detects if any open connection exists in the line and to what extent valid equipment (that is. equipment that does not represent an open connection) is connected to the line's connector interface before the power line voltage is electronically switched on. The object of the invention is thus to provide an open circuit detector for connecting devices in seismic data acquisition systems. The detector according to the invention comprises two transformers, a test signal source and at least one detection device, and is characterized in that the transformers' primary windings are connected to the detection device(s) and the signal source to form a primary circuit for detection of impedance changes, specially those caused by an open circuit condition in the secondary circuit, and the transformers' secondary windings are connected to the connecting device to form a secondary circuit or loop. It is also an object of the invention to provide a method for detection of an open circuit in a connecting device in seismic data acquisition systems by means of a detector comprising two transformers, at least one signal source and at least one detection device. The method according to the invention is characterized by connecting the transformers' primary windings to the detection device(s) and the test signal source to form a primary circuit, connecting the transformers' secondary windings to the connecting device to form a secondary circuit or loop, detecting impedance changes in the secondary circuit, and determining an open circuit condition based on said detected impedance changes. The invention is based on definition of a closed loop over the connector interface, where the loop impedance changes significantly when the connector is closed. This is achieved according to the invention by means of transformers where one of the windings is in series with the power line (secondary circuit), thus not requiring any additional and dedicated pins or wires for the detection device itself, which lies in the primary circuit and is inductively coupled to the secondary circuit by means of the transformers. The described invention can be implemented as an integral part of the connector or of the nearest take-out. The physical location can be adapted to the basic construction of the land seismic system. The invention must also be implemented into the electronic modules as these control the main power distribution. Fig. 2 shows one detector D l operating in accordance with the basic principle of the invention. The complete system comprises several detectors working together for monitoring all connectors in a line cable. Detector D l comprises two transformers (TM,TS), the secondary sides (W2M, W2S) of which are connected in series with one of the power lines (L I), and form a closed loop or secondary circuit for induced AC test signals together with blocking capacitors (Cbl , Cb2). Detector D l comprises also control logic circuits (CLM, CLS) controlling the loop, which can be configured in several different ways and detection circuits (DCM. DCS). The concept will work for both AC and DC power feeding systems. For AC systems, the blocking capacitors (Cb l,Cb2) must be replaced by an LC circuit tuned to a specific test signal frequency. Each detector D l comprises in addition at least one. and preferably two signal sources (SSM,SSS) . Detector Dl comprises a master and a slave circuit for operation in two different modes. TM. SSM. CLM and DCM form a circuit operative in "master" mode, while TS, SSS. CLS and DCS form a circuit operative in "slave" mode. In master mode, signal source SSM emits a signal into the loop and detection circuit DCM using said "own" signal checks if only relevant equipment (that is. equipment that will not lead to an open connection) is connected, in other words if the loop is closed. In slave mode, detection circuit SSM in Dl is not emitting a signal and is only listening to the signal emitted from the signal source in another detector (master). The detection circuit must be able to work in both modes. When power is off, that is when the power line in the loop is not energised. detector D l must exhibit the expected impedance for the loop, making it possible for another activated detector (in master mode) to detect its presence (more specifically by R1 S in Fig. 3). A typical start-up procedure, after power up, could be as follows- 1 ) Dl listens to another detector emitting its test signal. If such a signal is received ("true") then Dl signals a "closed connector" (SSS is activated) and puts itself into slave mode (that is SSM is not activated). 2) If no signal is detected, Dl switches on its own test signal (SSM is activated) and tests for connection by verifying a proper loop impedance. The simplest solution for the logic is depicted in Fig.3. Signal source SSM comprises a current source iM, a switch S IM and a resistor RIM in parallel with the primary side W1M of transformer TM. Detection circuit DCM and control logic CLM are connected to the "switch" side of resistance RIM, so as to check voltage drop across RIM. In master mode S IM is closed, the load at the secondary side of transformer TM will thus cause a voltage drop across RIM, and an open connector will be detected as a specific voltage drop across RIM. In slave mode, switch S IM is open and a voltage drop across RIM will be caused by a master signal from a master signal source in another detector (not shown). D l will signal a "closed connector" by detecting if signal is above a certain threshold level. A more advanced solution that will increase the detection margins is depicted in FigJ. This is based on a combination of parallel and serial resonant circuits tuned to the test signal frequency. The two switches S I and S2 will be operated in the following ways: - At power off or when the detector is in slave mode: S lM=S2M=S l S=S2S=open. - In master mode: S lM=S2M=S l S=S2S=closed. CIM and L IM are tuned to resonate at the test signal frequency- This implies that when power is off or when detector is in slave mode the C 1M/L 1M will short-circuit the primary side of transformer TM. The same applies to C I S and L1 S. This results in a very low loop impedance for the primary loop. In theory, the secondary side of the transformer, for the detector emitting the test signal, will be seen as a short-circuit. In slave mode the test signal can optionally be monitored by measuring the test signal voltage across L 1 S. In master mode both S IM and S2M will be closed and C IM will be in parallel with C2M and the primary side of transformer TM. This will form a parallel resonance circuit for the test signal frequency, giving a high voltage across the tuned circuit when the connector is open. In another embodiment of the invention (modification of fig. 4) C IM is replaced by L IM. In master mode, S lM=S2M=closed, L IM, C2M and the primary windings of transformer WI S are tuned to EMs resonance frequency. These components form a parallel resonance circuit in series with RIM. In slave mode. S l S=S2S=open and C2S will constitute a low loop impedance, that will "flaten" the resonance tops on the master circuit. If disturbing noise from the power line is present, a more advanced test signal generation could be applied. One method is to apply coded signals (spread spectrum signals) and crosscorrelation techniques. This will however require a more complex electronic design and preferably also a microcontroller for signal processing.

Claims: PATENT CLAIMS 1. Open circuit detector for connecting devices in seismic data acquisition systems, comprising two transformers (TM.TS), at least one signal source and at least one detection device, characterized in that the transformers' primary windings (W1M, WIS) are connected to the detection device(s) and the signal source to form a primary circuit for detection of impedance changes, specially those caused by an open circuit condition in the secondary circuit, and the transformers' secondary windings (W2M. W2S) are connected to the connecting device to form a secondary circuit or loop. 2. Detector according to claim 1, characterized in that the connecting device is a connector and the transformers' (TM,TS) secondary windings are implemented as an integral part of the power feeding wires and pins of the connector. 3. Detector according to claim 1, characterized in that the connecting device is an electronic module and the transformers' (TM.TS) secondary windings are implemented as an integral part of the module. 4. Detector according to one of the preceding claims. characterized in that the primary circuit comprises a combination of serial and parallel resonance circuitry tuned to the applied test signal frequency. 5. Detector according to one of the preceding claims, characterized in that the test signal is an amplitude, frequency or spread spectrum modulated signal. 6. Detector according to claim 2, characterized in that one of the pins for the loop is a common return path. 7. Detector according to one of the preceding claims 1-5, characterized in that the return path for the loop is external to the connector interface. 8. Detector according to one of the preceding claims, c h a r a c t e r i z e d i n that it comprises a master circuit comprising master transformer (TM), signal source (SSM), detection circuit (DCM) and control logic (CLM), and a slave circuit comprising slave transformer (TS), signal source (SSS), detection circuit (DCS) and control logic (CLS), and that the detector can act in master mode, where the master signal source (SSM) emits a test signal, and in slave mode, where the signal source (SSS) is switched off and the detector is listening to an external test signal. 9. Method for detection of an open circuit in a connecting device in seismic data acquisition systems by means of a detector comprising two transformers (TM.TS), at least one signal source and at least one detection device. c h a r a c t e r i z e d by connecting the transformers' primary windings to the detection device(s) and the test signal source to form a primary circuit, connecting the transformers' secondary windings to the connecting device to form a secondary circuit or loop, detecting impedance changes in the secondary circuit, and determining an open circuit condition based on said detected impedance changes. 10. Method for detection of an open circuit according to claim 9. c h a r a c t e r i z e d in that a detector with a master circuit comprising master transformer (TM), signal source (SSM), detection circuit (DCM) and control logic (CLM), and a slave circuit comprising slave transformer (TS), signal source (SSS), detection circuit (DCS) and control logic (CLS) is used, that under certain predefined conditions the detector acts in master mode, the master signal source (SSM) emits a test signal and the master detection circuit (DCM) checks impedance change, and that in other predefined conditions, the detector acts in slave mode, that is upon reception of an external test signal, the signal source (SSS) is not activated.

Inventors: HATTELAND KJELL, HATTELAND, KJELL
Applicants: GECO AS, HATTELAND KJELL, HATTELAND, KJELL
Application year: 2000
Main classification: G01V
IPC codes: G01V1