One weigh to take a load off your mind
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The maximum fine for an overloading offence — axle or gross — is to more than double in a few weeks. With this in mind David Wilcox has been looking at the value of electronic on-board vehicle weighing systems
EY ARE OUT to get rloaded lorries. The three bo3 responsible for checking y weights (the Department of nsport via its traffic examrs, the council's trading stands officers and the police) ve promised renewed ssure and better co-ordinal.
.nd these are not just empty eats. The Department of nsport's expenditure on encement weighbridges has doubled in the current incial year and is expected to yet again next year. Recruitnt of traffic examiners rose in second half of 1982 and the cts of this are being felt as ir training period is corn pleted.
Not only are the chances of being caught for overloading far higher but so are the penalties. The Transport Act 1982 gave the go-ahead to raise the maximum fine for an overloading offence from £400 to £1,000 and this is expected to take effect on April 11.
There has also been pressure on the Magistrates' Association to take full advantage of the higher maximum fine. The Association of County Councils whose members employ the trading standards officers want stiffer fines imposed on the basis that the current average fines do not even cover the cost of checking lorry weights and bringing prosecutions, let alone compensate for added road damage.
This leaves the road haulage operator between the Devil and the deep blue sea. In the current economic climate he needs to maximise his vehicle's payload more than ever and yet if he oversteps the mark the consequences are likely to be very expensive.
Put this way, you can make out a good case for electronic on-board vehicle weighing equipment, which should help tread the fine line between underloading and overloading.
On-board vehicle weighing is not new but seems to be going through a revival with several new systems appearing in the last year or so. It is not an easy task to sell onboard weighing equipment; many fleet operators will slam the door in the salesman's face.
This hostility and scepticism is easily understood; most people agree that some of the earlier systems were, frankly, disastrous. For the most part they seem to have been launched in this country with insufficient development and were either inaccurate or unreliable.
There are two ways of looking at on-board vehicle weighing systems. The most basic approach is to treat the system principally as a low-abiding piece of equipment to prevent overloading, in which case a low cost, relatively simple type should fit the bill.
Alternatively, you can use it in a more positive manner to reduce underloading and increase productivity which will usually involve a more sophisicated and expensive system.
Those in favour of the more comprehensive "all singing, all dancing" electronic on-board weighing systems justify the extra cost by pointing out that the greater amount of information not only eliminates the chance of an axle or gross overload but also cuts out underloading and hence the system will pay for itself.
The economics and pay-back period will depend on the previous degree of underloading (one system manufacturer claims that 10-15 per cent is typical), the value of the load being carried and the number of trips made in one day — a high frequency shuttle-type tipper operation offers plenty of scope.
The other way in which the onboard weighing system can recoup its cost is by saving a vehicle journeys between the loading site and the weighbridge to either add or take off weight. The time saved may allow another complete trip to be made at the end of the day.
Whatever price you pay for a system it needs three essential qualities; reliability, repeatability and accuracy. On this last point, system manufacturers make various claims but what degree of accuracy is really needed?
Prosecutions for overloading are brought under the Road Traffic Acts of 1972 and 1974 and there is no percentage margin or tolerance built into these regulations. However, in practice action is not usually taken unless the overload — either axle or gross — exceeds five to 10 per cent (enforcement is not entirely consistent).
If a dynamic axle weigher is used there is a stipulated tolerance of 150kg for each axle and 150kg multiplied by the number of axles for the gross vehicle weight.
From these accepted tolerances it is evident that an on-board weighing system designed to prevent illegal overloading should ideally be accurate to within 150kg, which can be translated to plus or minus 1.5 per cent in the case of a 10.17 drive axle. Anything with an accuracy of better than five per cent will probably be sufficient to avoid prosecution.
Using the more comprehensive type of system designed to make optimum use of the payload potential, a tolerance of 150kg is not satisfactory if the system is really going to pay its way. You should bear in mind that the system itself can weigh around 50kg Which means the increase in payload must be at least this amount before real gains are achieved.
When examining percentage accuracy claims, beware of averaged-out figures. Readings that are sometimes high and sometimes low do not cancel each other out, they merely show inconsistency as well as inaccuracy.
On-board weighing systems can be divided into three basic parts; the sensors, the wiring and the display unit in the cab. The dashboard-mounted display unit is normally a relatively straightforward piece of electronics working in a fairly clean environment. Its role is to interpret and display the information relayed by the sensors and the display can either show the actual weight numerically or represent it graphically using lights.
Although the display unit looks the more interesting component it should not divert the buyer's attention from the sensors, which are the key to the system's accuracy and reliability. Invented in the 1930s, the electronic scnsor (a term covering strain guages, load cells and transducers, all of which serve the same purpose) is mounted on a load-bearing component such as the axle, suspension or chassis member and so is working in a hostile environment. It needs to be able to withstand dirt, water, vibration, steam cleaning and extremes of temperature, particularly if fitted to tippers on site work.
The price quoted for the sensor alone varies enormously — I discovered prices ranging from £40 to £600 and nobody could offer an entirely satisfactory reason for this vast discrepancy.
Accuracy will also depend greatly on the location and fixing of the sensors. Some systems are easily fitted by the average well-equipped operator while others should be entrusted to the system's manufacturer or agent which may entail extra downtime and fitting charges.
The need for initial and subsequent regular calibration also varies, with some systems claiming greater stability than others. Yearly or half-yearly recalibration is typical.
In the systems reviewed the axle-mounted sensors are bolted directly to the axle beam (or differential housing), tached to the axle with rn; straps or bolted onto mount feet that are welded to the a: If in doubt about welding a thing to an axle, check with chassis or axle manufacturer.
The largest market sector electronic on-board weigh systems currently exists amc tipper operators and other I carriers where the load does come in easily-defined units ; can be unevenly distributed.
The same is true where weighbridge used to check payload is not close to the lo ing point and excessive timE lost in returning to make lc adjustments.
Another potential market ists in the rigid distribut vehicle sector. A single sen mounted on the front axle highlight a front axle overlc that can occur (even when gross weight is legal) owing t diminishing load at the rear the vehicle as the delivery rot. progresses. If a particu vehicle is more subsceptible t rear axle overload because c long chassis overhang a r axle-mounted sensor will g protection.
From May 1 there could v be additional interest shown artic operators. The majority them who are moving up to tonnes will be using their ex ing two-axle tractive units v new triaxle trailers. This creases the likelihood overloading the tractive un drive axle because of higl kingpin loadings. Many of • weighing systems are able monitor kingpin loadings by v of sensors under the fifth wh is worthwhile checking that articular system does not iplicate unit/trailer inhangeability because the tors on the trailer axles have e tuned into the display unit le cab.
rith prices ranging from £250 £3,000 the systems need le careful choosing. It is )ably fair to say that the price 'early every one is volume sitive; the develpoment s are usually high and the e they sell the cheaper they JId become.
ndoubtedly, the best way of ssing them is to talk to rators who have experience -tem — only they can give a picture. That is not to say the manufacturers' claims false in any way; some rators report a higher degree ccuracy than the manufacrs expect.
)re are details of some s of electronic on-board cle weighing equipment; it A an exhaustive list.
load, Welmech (Staffs) Engiring, Saxon Works, Royal et, Fenton, Staffs.
ter first introducing its onrd vehicle weighing six years Welmech dropped the idea re-entered the market two
s ago with its PAC 1000 em.
his uses rather unusual sh-made sensors similar in earance to car shock ablers mounted vertically on axle itself. Two of these sducers will normally be )ed to the front axle while a le transducer secured to the differential casing is used on the drive axle.
The display unit in the cab can show total load plus individual axle loads and if a pre-set figure is exceeded an audible bleeper is triggered. An accuracy of two per cent is claimed, provided (like most systems) the vehicle is on flat and level ground.
To fit a two-axle rigid the system costs £625 plus £62 fitting — Welmech is currently establishing fitting agents. Price for an eight-wheeler system is around £1,000 and the PAC 1000 can also be used on artics. Recalibration is recommended every six months and the operator can either do it himself using an electronic meter (price £1,000£1,200) or let Welmech do it at a cost of £30 each time.
Welmech is also launching a simpler system using smaller transducers and a simplified display unit with a graphic type of readout. A column of lights indicates how near the axle is to its plated weight but does not give a numerical reading. This system will cost about £250 plus £30 fitting. Both systems carry a year's guarantee. recently became the UK distributor for Loadax weighing equipment. The simplest system is the L.O.D. which is primarily intended to detect illegal axle loadings. The main applications are on the front axle of a rigid distribution vehicle or under the fifth wheel on a tractive unit. Matchbox-size sensors are bolted directly to the axle using drilled and tapped holes and an accuracy of two per cent is claimed.
The cab display unit does not show digital readings but uses green, amber and red lights. The driver "trims" the unit to zero and sets the desired maximum axle weight, less a small tolerance; when this load is reached a light flashes and a buzzer sounds.
Price for the L.O.D. fitted to the front axle only (one sensor) is £495 including fitting, while a version to monitor kingpin loading on a tractive unit uses two sensors under the fifth wheel and costs £775, including fitting.
Purchasers of the L.O.D. can later upgrade it to the more sophisticated Loadax system which uses a digital display unit to indicate actual axle and gross or payload loadings to the nearest 100kg.
On a four-wheeler three sensors are normally used (one on the steering axle and two on the drive axle) and the price is £1,500 fitted; it is the same for a six-wheeler.
If the vehicle is a tipper, Loadax prefers to mount the rear sensors between the body and the chassis rather than on the axle. An eight-wheeler needs four sensors and this will cost £1,550 fitted. A four-axle artic system costs around £1,600.
Loadax is compatible with all types of suspension and actual operational accuracy figures on a Foden 8x4 tipper in service average plus or minus 0.5 per cent. The system is claimed to be exceptionally stable and can be easily re-trimmed by the driver. There is a year's guarantee. Norde is also in the process of setting up a network of fitting agents and hopes to have 30 by June.
Precision Loads, Craven House, Carleton New Road, Skipton, This company stresses that its systems are designed to improve productivity, not merely guard against illegal overloading. The main application is for tippers and in preference to axlemounted sensors the P.L. system uses four load cells sandwiched between the chassis and the body; on tippers the front two are either side of the tipping ram and there are two on the body hinge pins at the rear.
The company claims that the combination of this location plus the use of well-proven American load cells gives exceptional ac curacy and sensitivty. The readout is the nearest 10kg and a system in service on a four wheel tipper is working at better than 0.5 per cent accuracy.
The load cells are wired on two channels, one for the front pair and one for the rear pair. Although the total payload can be shown, the actual axle loads cannot be read directly from the display unit since the sensors are not on the axles themselves.
However, axle loadings can easily be ascertained: with the vehicle laden to its maximum front axle weight (checked by a weighbridge) note the readings from the two sensors on the front channel — whenever this reading is repeated in operation the driver knows that the front axle is at its maximum.
Precision Loads says that chassis-mounted sensors are less vulnerable than axlemounted ones and the flatness of the ground is not so crucial. The load cells themselves are very expensive (about £575 each} and make this one of the more costly systems. A four-cell system for any rigid costs £2,750 plus £150 fitting. A ticket printer in the cab is also available at an additional cost of £1,000. For tractive units two load cells are mounted under the fifth wheel and this will cost £1,600 plus fitting.
Although expensive, the P.L. system is claimed to be the most accurate and it carries a two year guarantee.
For the specific problem of front-axle overloads on distribution vehicles P.L. also offers a less sophisticated system using the more typical axle-mounted transducer bolted to mounting feet welded to the steering axle. Like other similar systems this does need level ground and P.L. says the accuracy is typically plus or minus one per cent if properly set up. This costs £995 plus £100 fitting.
Red Forge, Unit 5 Alders Drive, Moons Moat East, Redditch, Worm The Red Forge Axle Load Indicator is a low cost system to detect axle overloading and relies on measuring spring deflection. The fitment to the front axle involves a strap around the axle attached via a stainless steel linkage to the central spindle of the chassis-mounted sensor. As the axle moves up and down in relation to the chassis this turns the spindle and the degree of rotation is measured within the sensor by an optical encoder using a photo-electric cell. The attachment to the rear axle is via the differential housing bolts.
The display unit in the cab gives a graphic indication with two columns of lights, one for each axle. The system is set up so that the top (eleventh) light flashes red when the maximum axle load is reached. The bottom light will come on at 70 — 80 per cent of the axle load and successive lights will appear as load is added. A bleeeper is also linked to the top two to warn that full load is near before the eleventh light flashes and sounds a warning.
Red Forge says its accuracy claim to within five per cent is conservative. It is ideal for use on multi-leaf suspension but the more limited travel of monoleaf involves a more sensitive optical encoder.
Vehicles as varied as artics or one-ton vans can accept the Red Forge equipment and it was designed to be easily fitted by the operator. It is a bolt-on type of fitment that can be transferred to another vehicle and carries a year's guarantee.
Re-calibration is recommended after six months to check for spring settlement and then subsequently at yearly intervals. The operator can do this himself with the aid of a weighbridge. Examples of prices are £410 for a two-axle system and £746 for a four-axle artic.
Smiths Industries, Automotive Instrument Systems, 50 Oxgate Lane, Cricklewood, London, Smiths' electronic axle load indicator was developed in Germany and uses small Germanmade strain guages which are bolted to mounting feet welded to the axles.
The display unit can show individual axle loads, gross weight and payload to the nearest 100kg Smiths claims an accur acy to within plus or minus 1 per cent. There are two be versions of the equipment. C is a sigle-axle version which only monitor one-axle load and so uses a simplified disp unit; this costs £750 plus fittin A two-axle system, which ( also monitor gross and paylo costs £900 plus fittings. multi-axle applications t prices rises by £250 for ei additional axle.
This Smiths system is not s able for artic combinations though the sensors can be fit to a tractive unit's fifth wh coupling to monitor king loadings.
There is a year's guarant Smiths has 10 fitting agents k is beginning to sign up more.
Transquip International Trail( 15 Princewood Road, Cor
Transquip's T1000 electro axle weighing system uses combination of load cells uni the -fifth wheel coupling E axle-mounted transducers. 1 display unit in the cab has a digit light emitting diode disc) rising in 100kg incremen Prices are approximately for the display unit and £500 each axle sensed.