Use of Truvelo Electronic Vehicle Speed Timing Device
| DOI | 10.1177/0032258X8005300308 |
| Published date | 01 July 1980 |
| Date | 01 July 1980 |
| Author | R. A. Crabb |
| Subject Matter | Article |
R. A. CRABB, M.A., LL.B. (Cantab)
Chief
Prosecuting Solicitor
for
the County
of
Kent
USE OF TRUVELO ELECTRONIC
VEHICLE SPEED
TIMING
DEVICE
Readers might be interested in a case which took place at Ashford
Magistrates' Court early in February this year when there was an
unsuccessful challenge of this device by the defence. The defendant
had been summoned for speeding (45 m.p.h. in a 30 m.p.h. area) and
the police detected the defendant's speed by use of the Truvelo
device. This was the first challenge to the machine in the United
Kingdom.
The Truvelo machine, which was first commissioned by the Sussex
Police in this country, is not an alternative to radar and Vascar but a
complimentary method of speed detection working on an entirely
different principle,
It
uses two fine cable sensors stretched across a road just 1.55
metres apart, which feed information to a time/ distance calculator
concealed in a briefcase in a police car at the side of the road. The
calculator measures the time it takes the front wheels of a vehicle to
travel from the start detector to the stop detector and converts this
directly into m.p.h.
(or
k.p.h.). The speed is displayed on a digital
readout and then stored in a memory.
The device can be quickly set up and effectively concealed and
indeed it is capable of adaption so that aphotograph can be taken of
the target vehicle (showing the number plate) at the time the
commission of the offence, but the writer knows ofno policeforce in
this country which has made use of this possibility.
The device is basically an electronic stopwatch; when the front
wheels of a vehicle pass over the detector cables and thus apply
mechanical pressure on to them, the molecular structure of the
insulating material changes and generates an electronic impulse. The
impulse is fed into the instrument at about half the speed of light.
Inside the device the impulses (start and stop) are amplified, then
shaped (made into square waves) and used to open an electronic gate
(start pulse) and to close the gate (stop pulse). A crystal oscillator of
two MHz supplies pulses with an accurate time spacing of 0.1
millisecond. The electronic gate referred to above, for the time period
it is opened, allows a number of oscillator pulses to pass through. As
the pulses are generated with an exact spacing of 0.1 millisecond, the
275 Police Journal
Ju~1'
1980
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