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A speed and frequency substandard for tachograph calibration equipment
Forensic Science In temational, 24 t 1984 ) 8 l-86 Elsevier Scientific Publishers Ireland Ltd.
A SPEED AND FREQUENCY CALIBRATION EQWZ%fENT
SUBSTANDARD
81
FOR TACHOGRAPH
J.R. RUSSELL and R.F. LAMBOURN* The Metropolitan SE1 7LP (U.K.) (Received (Accepted
Police
Forensic
Science
Laboratory,
109 Lambeth
Road,
London
May l&1983) July 7, 1983)
Summary The process of calibrating a tachograph makes use of a mechanical head drive unit and an electronic clock tester. Both these devices should be checked against a standard at 6-month intervals. The design of such a substandard, based on a highly stable 1 MHz crystal oscillator, is described. Key words: Tachograph;
Calibration; Substandard
Introduction The compulsory use of tachographs by larger passenger and goods vehicles in the United Kingdom under European Economic Community legislation has made the analysis of tachograph recordings a regular part of investigat ions into road accidents and other incidents. In order that such a recording may be acceptable as reliable evidence in court proceedings, it is necessary to ensure that the tachograph installation which made it is operating correctly. EEC Regulation No 1463/70 requires that an installation should be calibrated by a competent agent to yield a precision of +4% in distance, +-6 km h-’ in speed and ~2 min/day in time, after which all connections in the system must be sealed. An inspection by the agent musf be carried out every 2 years, but a full check to ensure compliance with these maximum tolerances is only required every 6 years. The frequent occurrence in investigations of vehicles with broken or absent seals, and the occasional discovery of tachographs which are grossly out of calibration has caused the police in England and Wales to adopt a policy of checking the calibration whenever possible. Among the equipment used for this are two electronic devices. The first, usuakly called simply a
*To whom all correspondence
and reprint requests should be addressed.
0379-0738/84/$03.00 o 1984 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
‘Calibration Rig’, is a precisely controlled electric motor which is used to drive the tachograph at different rates across its range so that the recording for a known input may be found: examples are the Kienzle type 1601-17, and the Veeder Root Drive Unit DA7550. The second electronic device is a watch maker’s clock t.ester, which is used to check the running of the tachograph’s electronic clock: examples are the Portescap Vibrograf BZOQ and the Helmut Klein Timoscop. Both types of instrument are also used by the official calibration agencies. Although these instruments are, in our experience, quite robust, the need arises for their accuracy to be checked periodically. The British Department of Transport requires that the calibration agencies have their instruments checked every 6 months, the manufacturers of the instruments being responsible for the actual method used and the degree of tolerance permitted. This checking service is not readily available to the police, and in any case it was felt by the Forensic Science Service, -,*,,hich carries out the chart analysis. that the police equipment should be <*hecked to a higher degree of accuracy and that the facility should be available at very short notice to meet the needs <>fparticular cases, 21 device has thxrefore been constructed to act as a substandard against which the two types of calibration device may be checked.
Specification
for the calibration
The output
substandard
of the calibration rig is a rotating shaft connected to a flexible of rotation is 1000 rev./h for each km h-’ indicated. ‘l’hus ;I speed of 18 km h-’ is equivalent to a rate of 18,000 h-’ of 5 s-l. Our c*alibratic,n standard accepts the input from the flexible cable, to drive 3 disc, which is illuminated by a 5 Hz strobe flash. Under t,he action of the 51robtb, the marking on the disc (a white arrow on a black ground) app&rs stationary at speeds which are exact multiples of 18 km h-‘, enabling the output of the device to bc checked throughout its range, The maximum speed to be checked is 180 km h-l. In order to produce a shai>p image of the arrow on the disc, a bright light of short duration is required, and this is produced by a xenon flash tube. ‘There is a dark green filter over the disc which renders the arrow almost invisible under ambient light conditions. The clock tester operates by detecting, through an inductive pick-up, the 2 Hz pulse of the tachograph clock circuit. The calibration substandard simulates this pulse in a coil encapsulated at the end of a short lead. When :t culock tester detects this pulse it should show a neghgible loss or gain of time. Figure 1 shows the front of the finished instrument, and Fig. 2 shows t!le side with the case removed to reveal the disc and strobe assembly. drive c-able. The rate
83
Fig. 1. Front of instrument.
p”.--
.--..
c
_
_
-
b
Fig 2. Side of instrument,
with case removed to show disc and strobe assembly.
84 TEST 1HHz
OUTPUTS 2nz
SHZ
MAGNtT
L._i
-
Fig. 3. Block diagram of electronics.
Electronics The electronics are required to provide an accurate flash at 5 Hz and a magnetic pulse of 2 Hz. A I-MHz crystal oscillator in a crystal oven provides a reference square wave of 1 MHz accurate to 3 parts in 109, after a warm up period of about 1 h. The output from the crystal is fed into a TTL divider chain which provides outputs of 2 Hz and 5 Hz (Fig. 3). The three reference frequencies are buffered and are connected to sockets on th.e rear of the instrumem for cahbration purposes. Switch SW1 allows either the ~-HZ or ~-HZ square wave to be selected and a monostable circuit provides a negative going pulse of about 30-ms duration. Switch SW2 selects either flash or magnetic outr;ut and a third pole, unshown, selects an hour counter to measure the cumulative tube operation time. The flash tube chosen was one manufactured for use with a warning beacon and hence has a very long life. However, in order that false triggerings should not occur, the tube was underrun by about 60%. The worst case guaranteed life on the tube was 5 X 106 flashes, which gives a life of 250 h at 5 Hz or 700 h at 2 Hz. The trigger capacitor presented some problems, however, as at 15 PI’ it fell between the minimum value for photoflash capacitors and the maximum for polypropylene types. A standard electrolytic capacitor was therefore used as the ‘best compromise available. The thyristor trigger circuit is shown below in its entirety as it represents the only part of the circuit where component v:rlues are critical (Fig. 4). Opto-isolator Kl prevents thyristor pulses Being fed back onto the TTL logic. The relay driver IC2 provides sufficier .t drive for the gate of the trigger thyristsr THl. Cl is the electrolytic flash capacitor. The trigger capacitor C2, the trigger transformer TRl and the flash tube FTl are all
Fig. 4. Flash trigger circuit.
manufactured by Siemens Ltd., of Sunbury on Thames. These components are listed in Table 1. The magnetic pulse output is provided by a remote relay coil potted in Araldite. The relay coil is driven from the- second half of the dual relay driver used in the flash trigger circuit. Testing
The completed unit was soak tested at 5 Hz and after 925 h failure occurred: the lamp was seen to flash erratically and the unit was switched off. It was found on inspection that the flash capacitor Cl had failed and was leaking electrolyte. The flash tube was found to be in good working order. The flash tube and capacitor were replaced and the unit was passed on to TABLE 1 COMPONENTS LIST Crystal in crystal oven Flash trigger circuit ICl Opto-isolator IC2 Relay-driver Rl 220 n 25 W Cl Flash capacitor 15 rF 450 V electrolytic C2 Trigger capacitor Trigger assy TRl Trigger coil 1 THl Thyristor BTY 79-3OOR FTl Flash tube All other resistors: 0.5 W metal oxide.
1. Q. D. Type TS52 1 B29 R.S. R.S. R.S. R.S.
Type Type Type Type
307-963 306-954 157-594 1037856
Siemens type K301 R.S. Type 262-387 Siemens type BUB0661
the National Physical Laboratory, is shown in the Appendix.
Teddington,
for evaluation. Their report
Conclusion The unit performed well against a theoretical life of 250 h. However, it is recommended that the flash tube and flash capacitor both be changed at 200-h intervals to maintain stability. Appendix The text of the National Physical Laboratory is as hollows:
Certificate
of Calibration
This equipment contains a P-MHz temperature controlled quartz crystal oscillator. The l-MHz signal is divided to produce output frequencies of 5 Hz and 2 Hz, which are also used to drive a strobe flash. The frequency of the crystal oscillator was set to nominal, after a warm-up period of 1 h: the frequencies of the ~-HZ and ~-HZ outputs were determined both directly and via observations of the flash tube. The results are given below. The frequency of the l-MHz crystal oscillator source was set to agree with the LLiboratory standard to within 1 part in lo*. Output Frequencies
2 Hz 5 Hz 2 Hz 5 Hz
rear output rear output flash output flash output
= 2.000 000 Hz * 0.000 = 5.000 000 Hz f 0.000 = 2.000 00 Hz + 0.000 = 5.000 00 Hz + 0.000
001 Hz 001 Hz 01 Hz 01 Hz
A SPEED AND FREQUENCY CALIBRATION EQWZ%fENT
SUBSTANDARD
81
FOR TACHOGRAPH
J.R. RUSSELL and R.F. LAMBOURN* The Metropolitan SE1 7LP (U.K.) (Received (Accepted
Police
Forensic
Science
Laboratory,
109 Lambeth
Road,
London
May l&1983) July 7, 1983)
Summary The process of calibrating a tachograph makes use of a mechanical head drive unit and an electronic clock tester. Both these devices should be checked against a standard at 6-month intervals. The design of such a substandard, based on a highly stable 1 MHz crystal oscillator, is described. Key words: Tachograph;
Calibration; Substandard
Introduction The compulsory use of tachographs by larger passenger and goods vehicles in the United Kingdom under European Economic Community legislation has made the analysis of tachograph recordings a regular part of investigat ions into road accidents and other incidents. In order that such a recording may be acceptable as reliable evidence in court proceedings, it is necessary to ensure that the tachograph installation which made it is operating correctly. EEC Regulation No 1463/70 requires that an installation should be calibrated by a competent agent to yield a precision of +4% in distance, +-6 km h-’ in speed and ~2 min/day in time, after which all connections in the system must be sealed. An inspection by the agent musf be carried out every 2 years, but a full check to ensure compliance with these maximum tolerances is only required every 6 years. The frequent occurrence in investigations of vehicles with broken or absent seals, and the occasional discovery of tachographs which are grossly out of calibration has caused the police in England and Wales to adopt a policy of checking the calibration whenever possible. Among the equipment used for this are two electronic devices. The first, usuakly called simply a
*To whom all correspondence
and reprint requests should be addressed.
0379-0738/84/$03.00 o 1984 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
‘Calibration Rig’, is a precisely controlled electric motor which is used to drive the tachograph at different rates across its range so that the recording for a known input may be found: examples are the Kienzle type 1601-17, and the Veeder Root Drive Unit DA7550. The second electronic device is a watch maker’s clock t.ester, which is used to check the running of the tachograph’s electronic clock: examples are the Portescap Vibrograf BZOQ and the Helmut Klein Timoscop. Both types of instrument are also used by the official calibration agencies. Although these instruments are, in our experience, quite robust, the need arises for their accuracy to be checked periodically. The British Department of Transport requires that the calibration agencies have their instruments checked every 6 months, the manufacturers of the instruments being responsible for the actual method used and the degree of tolerance permitted. This checking service is not readily available to the police, and in any case it was felt by the Forensic Science Service, -,*,,hich carries out the chart analysis. that the police equipment should be <*hecked to a higher degree of accuracy and that the facility should be available at very short notice to meet the needs <>fparticular cases, 21 device has thxrefore been constructed to act as a substandard against which the two types of calibration device may be checked.
Specification
for the calibration
The output
substandard
of the calibration rig is a rotating shaft connected to a flexible of rotation is 1000 rev./h for each km h-’ indicated. ‘l’hus ;I speed of 18 km h-’ is equivalent to a rate of 18,000 h-’ of 5 s-l. Our c*alibratic,n standard accepts the input from the flexible cable, to drive 3 disc, which is illuminated by a 5 Hz strobe flash. Under t,he action of the 51robtb, the marking on the disc (a white arrow on a black ground) app&rs stationary at speeds which are exact multiples of 18 km h-‘, enabling the output of the device to bc checked throughout its range, The maximum speed to be checked is 180 km h-l. In order to produce a shai>p image of the arrow on the disc, a bright light of short duration is required, and this is produced by a xenon flash tube. ‘There is a dark green filter over the disc which renders the arrow almost invisible under ambient light conditions. The clock tester operates by detecting, through an inductive pick-up, the 2 Hz pulse of the tachograph clock circuit. The calibration substandard simulates this pulse in a coil encapsulated at the end of a short lead. When :t culock tester detects this pulse it should show a neghgible loss or gain of time. Figure 1 shows the front of the finished instrument, and Fig. 2 shows t!le side with the case removed to reveal the disc and strobe assembly. drive c-able. The rate
83
Fig. 1. Front of instrument.
p”.--
.--..
c
_
_
-
b
Fig 2. Side of instrument,
with case removed to show disc and strobe assembly.
84 TEST 1HHz
OUTPUTS 2nz
SHZ
MAGNtT
L._i
-
Fig. 3. Block diagram of electronics.
Electronics The electronics are required to provide an accurate flash at 5 Hz and a magnetic pulse of 2 Hz. A I-MHz crystal oscillator in a crystal oven provides a reference square wave of 1 MHz accurate to 3 parts in 109, after a warm up period of about 1 h. The output from the crystal is fed into a TTL divider chain which provides outputs of 2 Hz and 5 Hz (Fig. 3). The three reference frequencies are buffered and are connected to sockets on th.e rear of the instrumem for cahbration purposes. Switch SW1 allows either the ~-HZ or ~-HZ square wave to be selected and a monostable circuit provides a negative going pulse of about 30-ms duration. Switch SW2 selects either flash or magnetic outr;ut and a third pole, unshown, selects an hour counter to measure the cumulative tube operation time. The flash tube chosen was one manufactured for use with a warning beacon and hence has a very long life. However, in order that false triggerings should not occur, the tube was underrun by about 60%. The worst case guaranteed life on the tube was 5 X 106 flashes, which gives a life of 250 h at 5 Hz or 700 h at 2 Hz. The trigger capacitor presented some problems, however, as at 15 PI’ it fell between the minimum value for photoflash capacitors and the maximum for polypropylene types. A standard electrolytic capacitor was therefore used as the ‘best compromise available. The thyristor trigger circuit is shown below in its entirety as it represents the only part of the circuit where component v:rlues are critical (Fig. 4). Opto-isolator Kl prevents thyristor pulses Being fed back onto the TTL logic. The relay driver IC2 provides sufficier .t drive for the gate of the trigger thyristsr THl. Cl is the electrolytic flash capacitor. The trigger capacitor C2, the trigger transformer TRl and the flash tube FTl are all
Fig. 4. Flash trigger circuit.
manufactured by Siemens Ltd., of Sunbury on Thames. These components are listed in Table 1. The magnetic pulse output is provided by a remote relay coil potted in Araldite. The relay coil is driven from the- second half of the dual relay driver used in the flash trigger circuit. Testing
The completed unit was soak tested at 5 Hz and after 925 h failure occurred: the lamp was seen to flash erratically and the unit was switched off. It was found on inspection that the flash capacitor Cl had failed and was leaking electrolyte. The flash tube was found to be in good working order. The flash tube and capacitor were replaced and the unit was passed on to TABLE 1 COMPONENTS LIST Crystal in crystal oven Flash trigger circuit ICl Opto-isolator IC2 Relay-driver Rl 220 n 25 W Cl Flash capacitor 15 rF 450 V electrolytic C2 Trigger capacitor Trigger assy TRl Trigger coil 1 THl Thyristor BTY 79-3OOR FTl Flash tube All other resistors: 0.5 W metal oxide.
1. Q. D. Type TS52 1 B29 R.S. R.S. R.S. R.S.
Type Type Type Type
307-963 306-954 157-594 1037856
Siemens type K301 R.S. Type 262-387 Siemens type BUB0661
the National Physical Laboratory, is shown in the Appendix.
Teddington,
for evaluation. Their report
Conclusion The unit performed well against a theoretical life of 250 h. However, it is recommended that the flash tube and flash capacitor both be changed at 200-h intervals to maintain stability. Appendix The text of the National Physical Laboratory is as hollows:
Certificate
of Calibration
This equipment contains a P-MHz temperature controlled quartz crystal oscillator. The l-MHz signal is divided to produce output frequencies of 5 Hz and 2 Hz, which are also used to drive a strobe flash. The frequency of the crystal oscillator was set to nominal, after a warm-up period of 1 h: the frequencies of the ~-HZ and ~-HZ outputs were determined both directly and via observations of the flash tube. The results are given below. The frequency of the l-MHz crystal oscillator source was set to agree with the LLiboratory standard to within 1 part in lo*. Output Frequencies
2 Hz 5 Hz 2 Hz 5 Hz
rear output rear output flash output flash output
= 2.000 000 Hz * 0.000 = 5.000 000 Hz f 0.000 = 2.000 00 Hz + 0.000 = 5.000 00 Hz + 0.000
001 Hz 001 Hz 01 Hz 01 Hz