GB2329717A

GB2329717A - Insulated joint tester

Info

Publication number: GB2329717A
Application number: GB9817131A
Authority: GB
Inventors: Christopher Hough
Original assignee: G T RAILWAY MAINTENANCE LIMITE
Current assignee: G T RAILWAY MAINTENANCE LIMITE
Priority date: 1997-08-09
Filing date: 1998-08-07
Publication date: 1999-03-31
Anticipated expiration: 2018-08-07
Also published as: GB2329717B; GB9817131D0; GB9716827D0

Abstract

An apparatus 1 for testing insulated rail joints 7 comprises a housing 2 containing a power source and associated electronic circuitry. The apparatus 1 further comprises of two leads 9. A probe 4 is connected to one of the leads 9 and a magnetic terminal 14 is connected to the other lead 9. An LED display panel 8 indicates, in a qualitative manner, the impedance across the joint 7 once the test has been carried out. The apparatus may also include a low battery warning system.

Description

INSULATED JOINT TESTER The present invention relates to apparatus for testing insulated jOintS. The present invention is described with particular reference to apparatus for testing insulated rail joints (which form an integral part of train detection rail circuits) but is not intended to be limited thereto. For example, apparatus according to the present invention can also be used to test point insulation and channel rodding insulation.

An insulated rail joint generally comprises a layer of an electrically-insulating material secured between the end-surfaces of abutting rails on a rail track or other permanent way. The insulating material used can be, for example a resin (such as a phenolic resin), a glass laminate, wood or a plastics material.

Existing methods of testing insulated rail joints have generally involved the use of a multimeter to measure the voltage across a joint.

From that voltage, the quality of the insulated rail joint must then be derived by manual, comparative calculations.

Problems arising during testing of insulated rail joints using a multimeter have been found to include inaccurate and/or non-reproducible readings (obtained because of a poor contact between the probes of the multimeter and the rails) and unreliable results because of human errors occurring during the calculations.

Furthermore, existing test apparatus which include multimeters can only be used to test D.C. circuits as a constant voltage is required across the joint and therefore their utility is limited.

The object of the present invention is to provide equipment for testing insulated rail joints in all types of track circuits.

According to a first aspect the present invention provides an apparatus for testing insulated rail joints, said apparatus comprising a power source which is operatively associated with means to contact the rail on either side of the joint, with means to measure impedance across the joint and with means to display, in a qualitative manner, the result of the measurement.

Preferably the apparatus further comprises a housing to prevent the ingress of moisture and/or dust, allowing the apparatus to be used outdoors in all weather conditions. The housing may include a handle or a strap to enable it to be carried by the user.

The power source is preferably a battery-energised power oscillator having an output of from 10-100kHz, for example 40kHz, which is operatively associated with a power amplifier. The output from the power source is preferably 5-15 Volts(rms) into a load of 2-4 Ohms, suitably 10 Volts(rms) into a load of 3 ohms.

The means to contact the rail on either side of the joint preferably comprises at least one probe. The or each probe may be made from metal, preferably mild steel. The or each probe is preferably provided with a sharp point which enables it to be made to exert maximum pressure on the rail surface, thus maximising electrical contact with the rail.

The means to contact the rail on either side of the joint preferably comprises one probe and one securing means whereby a terminal can be removably secured to the rail.

Preferably the securing means includes a magnet, which may be a permanent magnet or an electro-magnet.

The means to measure impedance across the joint preferably includes an amplifier operatively associated with a precision rectifier and with a low-pass filter. The impedance measuring means produces a d.c. voltage output proportional to the insulated rail joint current from an input voltage signal developed in the return path from the insulated rail joint to the power source.

The apparatus further comprises at least one, and preferably two, comparators. Preferably the comparators have predetermined upper and lower resistance or impedance thresholds. The upper resistance threshold is preferably in the range 10-15 ohms and the lower resistance threshold is preferably in the region of 4 ohms. Most preferably the upper resistance threshold is 10 ohms and the lower resistance threshold is 4 ohms.

The result display means preferably comprises at least one LED and the display may comprise one or more words (e.g. "PASS" or FAIL"); alternatively the display may comprise one or more colours (e.g. red, amber, green).

The display means is preferably controlled by at least one logic circuit.

Means (for example, one or more capacitors) may be provided to protect the apparatus from traction currents which could cause damage. A surge-arrestor may also be provided to help protect the apparatus against short-duration traction currents.

Apparatus according to the present invention can be used to test an insulated joint in any type of rail circuit owing to the fact that it has its own power source and does not rely on the presence of a voltage across the joint being tested.

A battery-check circuit may be provided to ensure that the or each battery is properly charged. A third LED may form part of the batterycheck circuit to indicate a low battery supply.

The apparatus may be provided with mean to filter out pulsing effects of High Voltage Input (HVI) track circuits.

According to a second aspect the present invention provides a method of testing an insulated rail joint with an apparatus according to the first aspect of the present invention (as hereinbefore described), in which the method comprises disposing the apparatus relative to the rail such that at least one of the first set of probes is in operative contact with the rail on each side of the joint, activating the power source to initiate the measurement of impedance across the joint and reading the display means to determine the result.

The present invention will be illustrated by way of example only, with reference to the accompanying drawings in which: - Figure 1 is a perspective view of an apparatus according to the first aspect of the present invention; Figure 2 is a schematic block diagram of the circuitry associated with the apparatus of Figure 1.

Figures 3a-c show the circuitry making up the IRJ Tester of the present invention; Figure 4 shows the power amplifier circuit; Figure 5 shows the battery check circuit; Figure 6 shows the layout of the electronics board; Figure 7 shows the layout of the power amplifier board; Figure 8 shows the layout of the battery check circuit; and Figure 9 shows the interconnection circuitry for the IRJ Tester.

Table 1 provides details of the components in the circuits of the IRJ Tester of the present invention.

In Figure 1, an insulated rail joint tester 1 comprises a housing 2 having a power source 2a and containing associated electronic circuitry.

The tester 1 further includes two leads 9, both of which are operatively connected to the circuitry contained in housing 2. One of the leads is attached, at its end remote from the housing, to a probe 4 and the other lead is attached, again at its end remote from the housing, to a magnetic terminal 14. The housing 2 includes an LED display panel 8 which is adapted to indicate the quality of the joint 7 after the test has been carried out by means of coloured LED's 8a. The panel 8 includes LED's 8c associated with a battery check circuit and an on/off switch 8b.

In use the probe 4 and magnetic terminal 14 are placed in contact with a rail 6, one on either side of the insulated rail joint 7 and the power source is activated to initiate the measurement of the impedance across the joint 7. This measurement is converted to a signal displayed on panel 8.

Referring now to Figure 2, the IRJ tester is energised from the 40kHz power oscillator formed by the oscillators IC 1 and the power amplifier IC 18. This is capable of delivering an output of 10V (rms) into a 3Q load. Contact with the rails on either side of the IRJ is made by way of probe 4 and magnetic terminal 14 being pressed onto the rail surfaces 6 as described in relation to Figure 1 (above).

The voltage developed across the 1Q resistor Rcs in the return path from the IRJ to the power oscillator is used to derive the current flow through the IRJ. This voltage generates a signal which is fed through the amplifier, precision rectifier and low-pass filter formed by IC 4 and IC 5 to produce a d.c. voltage output proportional to the IRJ current. This output is fed to comparators IC 6/b and IC 6/a (having respectively lower and upper thresholds set initially at levels equivalent to 4Q and 10n).

The outputs from the comparators are fed through logic circuits IC 7 and IC 8 and LED buffer circuits to activate a red LED if the IRJ impedance is less than 4Q, a yellow LED if between 4Q and 10Q, and a green LED if greater than 10Q. The LEDs are indicated generally at 9.

To protect the low-impedance power circuit of the IRJ tester from being damaged by traction currents, which may be flowing in the rails in some localities, the tester is de-coupled via a lOpF 450 V a.c. capacitor (C51). At 40 kHz this represents an impedance of only 0.5Q. An MOV surge arrestor, clamping at under 600 V, protects against short-duration high-voltage transients should these occur across the rails.

Further protection for the circuit is provided by means of a 47nF 1000 V d.c. capacitor C56 and an inductance L1.

The 1.2 Ampere.hour rating of the battery supply is generally considered adequate for one day's usage of the apparatus before recharging is necessary. It is envisaged that a number of IRJs may be inspected at a given site. The apparatus would be switched off for travelling between sites and during long periods of inactivity on any one site. At each IRJ several repeat measurements might be made, the tester being removed and repositioned between tests.

The 40kHz signal oscillator has low energy-consumption and is therefore allowed to operate continuously when the apparatus is switched on. On the other hand, the power amplifier has high energy-consumption and is activated for only one second's duration at each measurement.

Activation of the power amplifier is controlled by switch SW 1 and the (one second) monostable multi-vibrator IC 9. To allow sufficient time for the operator to register the result of the test, the logic circuits and LED displays remain active for 10 seconds, controlled by monostable multivibrators IC 11, IC 12 and IC 13.

In Figures 3a and 3b IC 1 and its associated components form the 40 kHz sinusoidal signal oscillators. Resistors R1, R2 and R3 are identical in value. Similarly, capacitors C1, C2 and C3 are identical in value. The resistance and capacitance values determine the oscillator frequency. R1, R2 and R3 are select-on-test resistors and if the frequency is to be changed, all three resistors should be changed accordingly. The resistors as fitted give an oscillator frequency of 40 kHz. The resistor values may be scaled appropriately for operation on any other desired frequency in the range of 10 kHz to 100 kHz. The output of this oscillator at IC 1/1 (IC 1 pin 1) is applied to the signal switch IC 2/1. The signal switch is enabled whenever the 1-second mono-stable multivibrator IC 9 is triggered and the switch connection between IC 2 pins 1 and 8 is closed. The signal then becomes available at Con 1/5. Con 1/4 is zero V.

Con 1/5 and Con 1/4 are connected to Con 5/I and Con 5/4 of the power amplifier (Fig.4) respectively. IC 9 and its associated components form the 1-second monostable multivibrator. A momentary push-button switch SW 1 is connected between Con 211 and Con 2/2 (Figure 2.). When this is pressed, the mono-stable multivibrator is triggered and produces a onesecond pulse at its two outputs. A positive going pulse is produced at IC 9/6 and a negative going pulse is produced at IC 9/7. IC 9/7 is normally at +5 V and when triggered goes to zero V for one second and enables the signal switch IC 2. The function of the one-second mono-stable multivibrator is to enable a measurement to be carried out. During that time a signal is applied to the power amplifier (Fig.4), formed by IC 18 and its associated components.

IC 18 (as illustrated in Figure 4) is the major source of power consumption and is enabled only for one second at a time to conserve power. IC 18 produces a voltage limited to 10 V rms output at IC 18/8.

Resistor RCL sets the current limit to 5 amperes. Diodes D 16 and D 17 protect the power amplifier from externally-imposed voltage transients.

The amplifier output is available at Con 5/3. The configuration of the amplifier feeding the IRJ test piece, the current-sensing arrangement and the voltage feed back signal is shown in Figures 2 and 9. IC 18 is mounted on a heat-sink which is for location purposes only because the mean dissipation is low. The amplifier output is coupled to the IRJ test piece via a 10 pF 450 V panel-mounted capacitor (C51). MOV is a 230 V 460 J metal oxide varistor which is also panel-mounted. Con 7 is a waterproof connector mounted on the box. From Con 7, a twisted pair of leads enables connection to be made to the IRJ test piece via the probe head.

The current passing through the IRJ is monitored by the seriesconnected resistor RCS (see Figure 3a). The amplitude of the voltage signal across this resistor is a measure of impedance (and hence quality) of the IRJ. The reject threshold of IRJ is about 4 ohms and the value of Rcs (1 ohm) is much smaller. It is noted that the absence, or reducedvalue amplitude, of the voltage feedback signal represents loss of signal from, or poor contact with, the rails of the IRJ.

The voltage developed across resistor RCS is applied to a differential amplifier. IC 4/a and its associated components form a differential amplifier with a gain of 2.1. Capacitors C13, C14, C15 and C16 provide high frequency roll-off. The upper 3dB bandwidth is approximately 150 kHz. All the resistors associated with the differential amplifier are 0.1 % high stability resistors to provide defined gain and improve the common mode rejection. IC 4/b is another amplifier stage whose gain can be adjusted by the select-on-test resistor R14. The output at IC 4/7 is fed to a precision full-wave rectifier consisting of IC 5/a, IC 5/b and associated components. It converts the bipolar 40 kHz sinusoidal signal into a fullwave rectified signal. The rectified output at IC 5/7 is applied to a lowpass filter consisting of resistor R21 and capacitor C21. The d.c. output at C21 is a measure of the peak amplitude of the signal developed across Rcs- The d.c. output of the low pass filter is applied as an input to two comparators (see Figure 3b). IC 6/a and associated components form the upper threshold comparator. IC 6/lb and associated components form the lower threshold comparator. IC 6/1 output is zero V when the IRJ impedance is above 4 ohms and switches to + 18 V when the impedance falls below 4 ohms. The signal applied to IC 6/3 through resistor R33 is compared against a stable reference applied to IC 6/2 through resistor R32. The stable reference can be altered by a select-on-test resistor R31 to change the lower threshold. Similarly the d.c. signal is applied to the upper threshold comparator through resistor R25. This is compared against a stable reference applied to IC 6/5 through resistor R24. The upper threshold can be altered by a select-on-test resistor R23. Below an IRJ impedance of 10 ohms IC 6/1 output will be zero V and will switch to + 18 V when the impedance rises to about 10 ohms. The two comparator outputs are transformed into logic compatible signals by resistive dividers. The two comparator outputs are inverted through IC 7/a and IC 7/b and gated through diodes D7 and D8 to produce the intermediate output when the IRJ impedance is between 4 and 10 ohms. When a measurement is not being made, the comparator outputs are in an illdefined state due to a lack of signal. The comparator outputs will be in the correct state only when a measurement is being made. Hence the three outputs are AND-gated through IC 8/b, IC 8/c and IC.8/d. The common gating signal is provided by the output of the one-second monostable multivibrator. Each AND-gate logic output is inverted and applied as a trigger signal to one of the three corresponding 10-second monostable multivibrators IC11, 1C12 and 1C13. Each of these monostable multivibrators is triggered by a low-level (zero V) signal at pin 1 and produces a logic high (5 V) output at pin 3 for 10 secs. The output drives a panel-mounted LED through a series resistor. Below 4 ohms, IC13 is triggered and drives the red LED. Above 10 ohms, IC12 is triggered and drives the green LED and, in between, IC11 is triggered and drives the amber LED.

Figure 3c shows the power supply and de-coupling arrangement for the various integrated circuits of Figures 3a and 3b. The dual-rail battery supplies of +18 V are applied through Con 6 and the ON/OFF switch shown in Figure 9 . IC 3 is a 5 V regulator and its output is used to power the 5 V logic circuits.

The battery check circuit is shown in Fig.5. IC19 produces a stable 5 V reference. The + 18 V battery voltage signal is attenuated by IC 17/a and is then compared against the reference in IC 17/b. Its output is positive as long as the battery voltage is above + 15 V. This output is coupled through resistor R81, diode D18 and panel-mounted red LED and "battery check +ve" momentary push-button switch. When the switch is pressed, the LED should light up if the battery voltage is above + 15 volts. Similarly, the -18 V battery voltage signal is inverted and attenuated by IC 16/a. The signal at IC 16a/1 is compared against the reference by comparator IC 16/b. The comparator output at IC 16b/7 will be positive if the magnitude of the negative rail is above 15 volts. This is applied through resistor R80, diode D19, a red LED and a "battery check -ve" momentary bush-button switch. When the switch is pressed, the LED will light up when the magnitude of the negative rail is above 15 volts.

Figures 6, 7 and 8 show the layout of the components of the electronics board, the power amplifier board and the battery-check circuit respectively. Figure 9 shows the overall interconnection between parts of the IRJ Tester unit including panel-mounted parts such as the LED indicators, ON/OFF switch and momentary push-button switches, all of which are well known and readily available to those skilled in the art to which the present invention relates.

Table 1. Component list - IRJ tester (Components sourced from RS Components Ltd. unless indicated) a. RESISTORS R1, R2, R3 3k92 0.1% 0.125W 166-300 R4, R5, R83 3k9 1% 0.25 W 148-641 R86, R85, R27, R33, R76 10k 1% 0.25 W 148-736 R6, R84, R24, R25, R32 R33, R60, R72, R77, R78, R82, R75, R69, R40 22k 1% 0.25 W 148-815 RCL 0.14R 1% 0.25 W 150-565 (7 x 1 RO in parallel) RCS OR5 1% Series/parallel arrangement R7, R8, R9, R10 6k8 0.1% 0.125W 166-560 R11, R12 28k7 0.1% 0.125 W 167-169 R13 5k6 1% 0.25 W 148-679 R14 9k1 1% 0.25 W 148-720 R15 15k 1% 0.25 W 148-770 R16, R17, R18, R20 11k8 0.1% 0.25 W 166-790 R19 5k9 0.1% 0.125 W 166-504 R55, R56, R57 2k2 1% 0.25 W 148-584 R22 4k3 1% 0.25 W 147-657 R23 560R 1% 0.25 W 148-449 R26, R71, R79 1M 1% 0.25W 149-228 R28, R36 560k 1% 0.25 W 149-161 R29, R37, R41, R42 220k 1% 0.25 W 149-060 R23, R30, R51, R52, R53 1k 1% 0.25W R80, R81 2k 1 % 0.25 W 148-578 R61, R62, R63 3k 1% 0.25 W R31 2k6 1% 0.25 W R34 470k 1% 0.25 W 149-972 R38, R54 100k 1% 0.25 W 148-972 R43, R44, R45, 75k 1% 0.25 W 148-944 R46, R47, R48 330R 1% 0.25 W 148-382 R66 1M 1% 0.25 W 149-228 R39 2M2 1% 0.6 W 336-749 (Fornell) R67 30k 1% 0.25 W 148-843 R68 3k6 1% 0.25W 148-635 R70 13k 1% 0.25W 148-764 R74 1k5 1% 0.25W 148-540 R21 4k7 1% 0.25 W Table 1 Component list - IRJ tester (continued) b. CAPACITORS C1, C2, C3 lnF 1% 250 V 115-477 C45 10 F 20% 6.3 V 207-3858 C13, C14, 220pF 1% 630V 115-528 C15, C16 47pF 1% 630 V 115-483 C58 1 F 5% 63V 169-1411 C26, C27, C28 0.47 F 5% 63 V 114-862 C31, C32, C33 47nF 5% 100V 115-966 C21 0.22F 5% 63V 114-856 C4, C5, C49, C50 100 F 20% 20 V 216-3024 C7 150 F 20% 6.3 V 216-2784 C6, C8, C9, C17, C18, C19, C20 C23, C24, C25, C10, C11, C12, C29 C30, C34, C35, C36, C22 C42, C43, C44, C45, C46 0.1 IlF 20% 68 V 126-556 C52, C53, C47, C48 10 F 20% 25V 207-4182 C51 10 F 10% 450 V 116-363 C54, C55 47 pF 2% 100 V 126-887 C56 0.1 F 20% 1500V c. DIODES D1 to D15, D18, D19 1N4148 D16, D17 SBYV28-200 196-0997 D20, D21 BYT01-400 366-470 (Farnell) ZD1, ZD2 5V6 (BZX79) 5% 0.4 W 283-665 (Matched at 5 mA current) d. INTEGRATED CIRCUITS 101, IC4, IC5, IC16, IC17 OP 275 GP 284-652 IC2 DG471DJ 656-552 IC3 LM2930T5.0 412-533 (Farnell) IC6 LM2903N 858-455 IC7 40106B 308-461 IC8 4081B 640-743 IC9 4538B 641-178 IC10, IC19 REF01HP 4110-309 IC11, CI12, CI13 ZN1034E 305-850 IC18 OPA541AP 428-048 Table 1 Component list - IRJ tester (continued) e. TRANSISTORS TR1, TR2, TR3 2N2222A 933-650 (Farnell) f. LED's LED 1 (Red) 743-987 (Farnell) LED 2 (Amber) 744-001 (Farnell) LED 3 (Green) 743-999 (Farnell) LED 4, LED 5 (Red) 743-835 (Farnell) 9. SWITCHES AND CONNECTORS SW1 (Start test) 414-772X (Farnell) SW2 (Battery check) 414-770D(Farnell) SW3 (Battery check) 414-771 B (Farnell) ON/OFF Switch 421 -885R (Farnell) Connector 6 (Battery box - electronic box) 035-803G/035-804E (Farnell) Connector 7 (Electronics box -output to IRI) 41 4-435A/4 14-441 E (Farnell) h. SURGE ARRESTOR MOV 230 V 460 J 218-777 (Farnell) i. BATTERIES 6 off 6 V 1.2 Ah 143-564 (Farnell) I. INDUCTOR L1 2.3 pH Custom built

Claims

CLAIMS 1. An apparatus for testing insulated rail joints, said apparatus comprising a power source which is operatively associated with means to contact the rail on either side of the joint, with means to measure impedance across the joint and with means to display, in a qualitative manner, the result of the measurement.
2. The apparatus according to Claim 1 further comprising a housing.
3. The apparatus according to Claim 2, wherein the housing includes a carrying handle or strap.
4. The apparatus according to any preceding claim, wherein the power source is a battery-energised power oscillator having an output of from 10 to 100 kHz which is operatively associated with a power amplifier.
5. The apparatus according to Claim 4, wherein the power source is a battery-energised 40kHz power oscillator which is operatively associated with a power amplifier.
6. The apparatus according to any preceding claim, wherein the output from the power source is 5-15 Volts (rms) into a load of 2-4 ohms.
7. The apparatus according to Claim 6, wherein the output from the power source is 10 Volts (rms) into a load of 3 ohms.
8. The apparatus according to any preceding claim, wherein the means to contact the rail on either side of the joint comprises at least one probe.
9. The apparatus according to Claim 8, wherein the or each probe is made from metal.
10. The apparatus according to Claim 9, wherein the metal is mild steel.
11. The apparatus according to any one of Claims 8 to 10, wherein the or each probe is provided with a sharp point which enables it to be made to exert maximum pressure on a surface of the rail.
12. The apparatus according to any one of Claims 8 to 11, wherein the means to contact the rail on either side of the joint comprises one probe and one securing means whereby a terminal can be removably secured to the rail.
13. The apparatus according to claim 12, wherein the securing means includes a magnet.
14. The apparatus according to Claim 13, wherein the magnet is a permanent magnet.
15. The apparatus according to Claim 13, wherein the magnet is an electro-magnet.
16. The apparatus according to any preceding claim, wherein the means to measure impendance across the joint includes an amplifier operatively associated with a precision rectifier and with a low-pass filter.
17. The apparatus of any preceding claim further comprising at least one comparator.
18. The apparatus according to Claim 17, wherein the at least one comparator has predetermined upper and lower resistance or impedance thresholds.
19. The apparatus according to Claim 18, wherein the upper resistance threshold is in the range 10-15 ohms and the lower resistance threshold is about 4 ohms.
20. The apparatus according to Claim 18 or 19, wherein the upper resistance threshold is 10 ohms and the lower resistance threshold is 4 ohms.
21. The apparatus according to any preceding claim, wherein the result display means comprises at least one LED.
22. The apparatus according to any preceding claim, wherein the display means comprises one or more words, or the display means comprises one or more colours.
23. The apparatus according to any preceding claim, wherein the display means is controlled by at least one logic circuit.
24. The apparatus according to any preceding claim, further comprising means to protect the apparatus from traction currents.
25. The apparatus according to Claim 24, wherein a surge-arrestor is provided to help protect the apparatus against short-duration traction currents.
26. The apparatus according to any one of Claims 4 to 25, wherein a battery-check circuit is provided to ensure that the or each battery is properly charged.
27. The apparatus according to Claim 26, wherein a third LED forms part of the battery-check circuit to indicate a low battery supply.
28. A method of testing an insulated rail joint with an apparatus according to any one of Claims 1 to 27, in which the method comprises disposing the apparatus relative to the rail such that at least one of the first set of probes is in operative contact with the rail on each side of the joint, activating the power source to initiate the measurement of impedance across the joint and reading the display means to determine the result.
29. An apparatus for testing insulated rail joints, substantially as described herein with reference to the accompanying drawings.
30. The method according to Claim 28 substantially as described herein.