GB2223851A

GB2223851A - Device for checking insulation resistance between earth and buried metal piping

Info

Publication number: GB2223851A
Application number: GB8912551A
Authority: GB
Inventors: Mauro Giuntoli
Original assignee: IL GAS SpA SOC IT
Current assignee: IL GAS SpA SOC IT
Priority date: 1988-10-14
Filing date: 1989-06-01
Publication date: 1990-04-18
Also published as: ES1011403U; IT215064Z2; FR2637986A3; ES1011403Y; GB8912551D0; IT8853466V0; FR2637986B3

Abstract

A device for checking the insulation resistance between earth D and buried metal piping T provided with an insulating covering and/or for cathodic protection of aforementioned buried piping, comprises: - A first, a second and a third terminal (t1-t3) for connecting respectively to the piping, to a buried reference electrode E and to an earth plate D, - A d.c. voltage source S which drives current between the first and the third terminal via the earth and the piping, and - A voltmeter V and an ammeter A connected respectively to measure the potential difference between the first and second terminal and the current flowing between the first and third terminal during operation. The device also comprises a feeder 2 connected to the first, second and third terminals and which produces a current between the first and third terminal such that the potential difference between the first and the second terminal, is kept constant and equal to a preset reference value. <IMAGE>

Description

The invention relates to a device for checking the insulation resistance between earth and buried metal piping provided with an insulating covering, comprising: - A first, a second and a third terminal for connecting respectively to the pimping, to a buried reference electrode and to an earth plate, - A d.c. voltage source adapted to convey current between the first and the third terminal via the earth and the piping, and - A voltmeter end an ammeter adapted respectively to measure the potential difference between the first and second terminal and the current flowing between the first and third terminal during operation.

The object of the invention is to improve the reliability of meesurement of a device of the aforementioned kind, more particularly when the circuit conditions very (variations in the resistivity of the ground, the charge of the battery, the surface area of the piping, etc.) According to the invention, this object is attained by constructing a device cf the aforementioned kind which also comprises a feeder connected to the first, second and third terminal and adapted to produce e current between the first and third terminal such thet the potential difference between the first end the second terminal is kept constant and equal to a preset reference value.

The device according to the invention may also advantageously be used for cathodic protection of piping, more particularly in areas effected by varying electric fields.

Other features and advantages of the invention will be clear from the followlng detailed description with reference to the accompanying drawing, which is provided by way of non-limitative example only and shows the electric circuit of a device according to the invention.

In the drawing, reference 1 denotes e device which serves the double purpose of checking the insulation of buried metal piping T and cathodic protection thereof. The device comprises a d.c. voltage source S comprising e.g. a 12-volt battery. The negative terminal of source S is connected to a first terminal tl of the device, with interposition of a switch I1 end a first pair of contacts of a double switch 12. An ammeter A is connected in series with the conductor which connects the terminal t1 to the negative terminal of source S, and two sockets b and bo are also provided for inserting an external ammeter if required. The terminal t1 of the device 1 is connected to a clip welded to the metal surface of piping T.Device 1 also has a terminal t2 connected to a reference electrode E with copper-copper sulphate contact with the earth, and a terminal t3 connected to an earth plate or point D inserted into the ground.

Device 1 also comprises a feeder 2 capable of maintaining a constant potential difference between terminals t1 and t2. Feeder 2 comprises an integrated circuit 3, e.g. of the kind known by the commercial designation L123, and a potentiometer P. The resistive component of potentiometer P is connected at one end to the foot 6 of circuit 3 and at the other end to the negative terminal of source S. The cursor of potentiometer P is connected to foot 5 of circuit 3. The foot 7 of circuit 3 is connected to the negative terminal of the supply source S, whereas feet 11 and 12 are connected to the positive terminal of source S with interposition of the other two contacts of the double switch 12.Foot 10 of circuit 3 is connected to terminal t3 with interposition of a resistor Rl for limiting the maximum output current of feeder 2. Foot 4 of circuit 3 is connected to terminal t with interposition of a current-limlting resistor R having a resistance of 1 kQ and a diode Dl for preventing reversal of the signal coming from terminal t through the integrated circuit 3.

The followlng components are disposed between terminal t and the negative terminal of source S: - A capacitor C for for filtering the signal from terminal t and having a capacitance of e.g. 100 nF, - A Zener diode D for limiting the signal from terminal t2, and havlng a threshold voltage of e.g. 7 V, - A resistor R3 and - A device Z, (Zenamic) for protecting the circuit which closes on the reference electrode E.

A voltmeter V is disposed between terminal t and terminal t, for measuring the potential difference between piping T and earth. Two sockets b1 and b2 are disposed in correspondence with terminals t1 and t in order to insert an external voltmeter if required. A protecting device Z2 (Zenamic) is disposed between terminals t3 and t1 for protecting the piping circuit and earth plate.

In operation, after closing the switches Il and I:, the potentiometer P is actuated so as to adjust the potential difference between piping T and the reference electrode E. The integrated circuit 3 generates a current such that the potential difference previously imposed between the piping and the electrode is kept rigidly constant, in spite of variations in the conditions of the piping-earth-earth plate circuit or variations in the electric fields in the ground.

The device according to the invention basically has the following three very wide possible applications: a) It can be used as a device for measuring the insulation between the piping and earth. In that case the supply source will be a battery and the switch I2 will be closed for only sufficient time to read the values indicated by the voltmeter and the ammeter.

Systematic readings are made during the work of laying the piping, in order to check any damage to the covering.

2) The device can also be used as a temporary feeder for cathodic protection. The device can be used for temporary protection of lengths of piping which cannot directly be connected to a piping network which already has cathodic protection.

The device is particularly useful in areas affected by variable electric fields, since it has the feature of maintaining a constant potential difference between the piping and the electrode. In that case the supply circuit will be a battery having sufficient capacity to operate independently for some months.

3) Finally the device can also be used as a permanent feeder of a cathode current for permanent cathodic protection of lengths of piping, more particularly piping affected by railway crossing. In that case the supply source can be an accumulator kept charged by photovoltaic panels.

Of course, wlthout altering the principle of the invention, the details of construction and the embodiments can vary widely from those described end illustrated without thereby departing from the scope of the invent ion.

Claims

1. A device of use for checking the insulation resistance between earth and buried metal piping provided with an insulating covering end/or for cathodic protection of aforementioned buried piping, comprising: - A first, a second and e third terminal for connecting respectively to the piping, to e buried reference electrode and to an earth plate, - A d.c. voltage source adapted to convey current between the first and the third terminal via the earth and the piping, end - A voltmeter and an amater adapted respectively to measure the potential difference between the first and second terminal and the current flowing between the first and third terminal during operation;; characterised in that it also comprises e feeder connected to the first, second and third terminal and adapted to produce a current between the first and third terminal such that the potential difference between the first and the second terminal, is kept constant and equal to a preset reference value.

2. A device according to claim 1, characterised in that the feeder also comprises a manual adjusting device for imposing the aforementioned reference value of the potential difference between the first and the second terminal.

3. A device according to claim I or claim 2, characterised in that a protective diode is disposed between the second terminal end the feeder to prevent a reversal of polarity of the voltage between the first and second terminal.

4. A device according to claim 3, characterised in thet a capacitor, a Zener diode, a resistor and a detector device are connected between tlie first and the second terminal.

5. A device according to claim 4, characterised in that currentlimiting resistors are connected between the feeder and the second and third terminal respectively.

6. A device according to claim 5, characterised in that a protective device is connected between the first and the second terminal.

7. A device substantially as hereinbefore described and illustrated in the accompanying drawings.