FR2637986A3 - INSULATION RESISTANCE TESTING DEVICE - Google Patents

Abstract

A device for checking the insulation resistance between a buried metal pipe T provided with an insulating coating and the earth and / or for the cathodic protection of a buried pipe of this type, comprises: - a first T1, a second T2 and a third terminal T3 intended to be connected respectively to the tube T, to a buried reference electrode E and to an earth connection D, - a DC voltage source S able to determine the passage of a current between the first and the third terminal through the earth and the pipe, and - a regulator 2 connected to said first, second and third terminals and able to deliver between the first and the third terminal t1, t3 a current of an intensity such as the potential difference between the first and the second terminal t1, t2 is kept constant and equal to a predetermined reference value.

Description

RESISTANCE MONITORING DEVICE

ISOLATION

  The present invention relates to a device for controlling the insulation resistance between a buried metal pipe provided with an insulating coating and the ground, comprising: - a first, a second and a third terminal intended to be connected respectively to the pipe, to a reference electrode in contact with the ground and to an earth connection, - a DC voltage source capable of determining the passage of a current between the first and the third terminal through the ground and the pipe, - a voltmeter and an ammeter capable of measuring respectively the potential difference between said first and second terminals and the current flowing between said first and third

terminals during operation.

  The object of the present invention is to improve the measurement reliability of a device of the type described above, in particular when the characteristics of the circuit vary (modification of the resistivity of the ground, of the charge of the battery, of the surface of the

tubing, etc.).

  According to the present invention, this objective is achieved by manufacturing a device of the type defined above which further comprises a regulator connected to said first, second and third terminals and capable of delivering between the first and the third terminals a current of such intensity that the potential difference between the first and the third terminals is kept constant and equal to a value of

predetermined reference.

  The device according to the present invention can also be advantageously used for cathodic protection of pipes, in particular in areas subject to variable electric fields. Additional features and advantages of the present invention

  will appear more clearly from the description

  detailed below with reference to the attached drawing, which illustrates the electrical diagram of a

  device according to the present invention.

  In the drawing, the reference 1 designates a device which performs the dual function of controlling the insulation of a buried metal tube designated by T - and of cathodic protection of the latter. The device 1 comprises a DC voltage source S,

  consisting for example of a 12 volt battery.

  The negative pole of the source S is connected to a first terminal of the device designated by t ", a switch I, and a first pair of contacts of a second switch I2 being arranged between the pole and the first terminal. On the conductor which connects the terminal t, to the negative pole of the source S is connected in series an ammeter A and two sockets b3 and b4 are also provided for the

  possible connection of an external ammeter.

  Terminal t of device 1 is connected to a stud welded to the metal surface of tubing T. Device 1 is provided with two other terminals designated by t2 and t3 connected respectively to a reference electrode E made of copper-copper sulphate in contact with the ground and at a socket

  earth or point D stuck in the ground.

  The device 1 is further provided with a regulator 2 capable of keeping the potential difference constant between the terminals t, and t2. The regulator 2 comprises an integrated circuit 3, for example of the type known under the commercial symbol L 123, and a potentiometer P. The resistive element of the potentiometer P is connected on one side to the tab 6 of the circuit 3 and of the other to the negative pole of the source S. The potentiometer cursor P is connected to the lug 5 of the circuit 3. The lug 7 of the circuit 3 is connected to the negative pole of the power source S while the lugs 11 and 12 are connected to the positive pole of the source S, the two other contacts of the double switch I2 being arranged between these two tabs. The lug 10 of the circuit 3 is connected to the terminal t3 and a resistor R, limiting the maximum current is interposed at the output of the regulator 2. The lug 4 of the circuit 3 is connected to the terminal t2 and a current limiting resistor R2, having a resistance of 1 kohm, and a diode D, intended to prevent the inversion of the signal coming from the terminal t2 on the integrated circuit 3 are interposed

between tab 4 and terminal t2.

  Between the terminal t2 and the negative pole of the source S are placed the following components - a capacitor C to filter the signal coming from the terminal t2, with a capacity of 100nF

for example,

  - a Zener diode D2 to limit the signal from terminal t2, having a threshold voltage of 7 volts for example, - a resistor R3, and - a device Z, (Zenamic) for the protection of the circuit which closes on the 'reference electrode E. Between terminal t2 and terminal t, a voltmeter V is placed to measure the potential difference between the tubing T and the earth. Two sockets designated by b1 and b2 are placed so as to correspond with the terminals t, and t2 for the possible connection of an external voltmeter. A Z2 protection device (Zenamic) for the protection of the tubing / earth circuit is placed between the terminals

t3 and t ,.

  In operation, after having closed the switches I and I2, the potentiometer P is actuated to adjust the potential difference between the tubing T and the reference electrode E. The integrated circuit 3 delivers a current whose nature is such that it keeps the potential difference between the tubing and the previously laid electrode rigorously constant, whether during variations in conditions of the tubing-earth-earth circuit or during variations in the electric fields in the

Earth.

  The device according to the invention essentially allows the following three different applications: 1) it can be used as a device for measuring the insulation between the pipe and the ground. In this case, a battery is used as the power source and the switch I2 is closed just the time necessary to read the values indicated by the voltmeter and the ammeter. Systematic readings are taken during the installation of the tubing in order to detect any damage to the coating. 2) The device can also be used as a temporary cathodic protection regulator: the device can be used for protection

Z63? 7986

  of parts of tubing that cannot be immediately connected to a network of tubing

already protected in cathode.

  The device is particularly useful in areas sensitive to variable electric fields thanks to its characteristic which allows it to keep the potential difference between the tubing and the electrode constant. In this case, the power source is constituted by a battery having a capacity such that it

  guarantees an autonomy of a few months.

  3) Finally, the device can also be used as a permanent cathodic supply regulator for the permanent cathodic protection of parts of tubing, in particular in the case of tubing cut by railways. In this case, an accumulator supported by panels can be used as a power source.

photovoltaic.

  Naturally, by not changing the principle of the invention, the particulars of manufacture and the forms of actuation can be largely modified with respect to the

  description and illustration without

  depart from the scope of the present invention.

Claims (6)

  1. Device which can be used for checking the insulation resistance between a buried metal pipe (T) provided with an insulating coating and the earth and / or for the cathodic protection of a pipe thus designed and buried, comprising: - a first (t,), a second (t2) and a third (t3) terminals intended to be connected 1C respectively to the tubing (T), to a buried reference electrode (E) and to an earth connection (D ), - a direct voltage source (S) capable of determining the passage of a current between the first and the third terminal through the ground and the pipe, - a voltmeter (V) and an ammeter (A) which can respectively measure the potential difference between said first and second terminals and the current flowing between said first and third terminals during operation; characterized in that it further comprises a regulator (2) connected to said first, second and third terminals and capable of delivering between said first and third (t3) terminals a current of an intensity such as the potential difference between the first and the second bound (t ,, t2) is kept constant and equal to one   predetermined reference value.   2. Device according to claim 1, characterized in that said regulator (2) further comprises a manually actuable regulation device (P) capable of allowing the definition of said reference value of the potential difference between the first and the second terminal.   3. Device according to claim 1 or claim 2, characterized in that a protective diode (Di) against reverse polarity between said first and second terminals is provided between said second terminal and said regulator (2).   4. Device according to claim 3, characterized in that a capacitor (C), a Zener diode (D2), a resistor (R3) and a protection device (Za) are connected between   said first and second terminals.   5. Device according to claim 4, characterized in that respective resistors (R2, R.) current limiting are connected between the regulator and said first and third terminals. 6. Device according to claim 5, characterized in that a protection device (Z2) is connected between said first and second terminals.   The assembly being substantially as described and   illustrated and for the specified objectives.