GB2227848A - Improvements relating to axle weight sensor calibration - Google Patents

Abstract

A vehicle axle load sensor is calibrated by lifting the vehicle body e.g. with a jack to remove the weight of the body from the sensor and calibrating the sensor to zero. The body is jacked up at different points in succession to enable each axle load sensor to be calibrated to zero. When jacked up a low profile accurate weighing machine is positioned under the wheel, and when the jack is released the weighing machine indicates the bearing weight of the wheel which provides a second calibration point for the axle load sensor. Further raising and lowering of the vehicle body enables further calibration points to be derived. <IMAGE>

Description

itImProvements relating to Sensor Calibration" Description This invention relates to sensor calibration.

It is primarily concerned with the calibration of sensors on vehicles which give an on-board indication of the vehicle's weight or loading.

Such sensors are generally mounted on the axle, and incorporate strain transducers which respond to deformation of the axle under load. They are usually positioned between each wheel and the adjacent suspension point, although they may be positioned between such points. In any event, there is a set of such sensors for any one vehicle to give its total weight or loading.

While such sensors can be made to be very responsive and accurate, the accuracy depend, when the sensor is fitted to the vehicle, on correct calibration.

A slight error in one sensor mirrored by similar errors in other sensors can add up to a considerable error in the total.

Hitherto, calibration methods have not been very satisfactory, or else have been difficult or tedious to perform. For example, a vehicle can be driven to a weighbridge, which would give an accurate total weight, and that could be related to the sum of the sensors' outputs. However, that does not indicate whether the individual sensors are correctly calibrated, and of course it only gives one result.

The relationship of a sensor output to the weight it is determining is sometimes linear, but more often a curve, so for calibration one needs to take at least two and preferably more readings with the sensor under different loadings.

It is the aim of this invention to provide a simple and effective method of achieving such calibration.

According to the present invention there is provided a method o calibrating a weight indicating sensor, the sensor being attached to a point on the body where the weight of the body itself normally produces a sensor output related to that weight, the method comprising exerting a lifting force on part of the body in a manner to counteract the weight thereof which affects the sensors, calibrating the sensor to zero, relieving, removing and/or reversing the lifting force while supporting said part of the body on an independent weighing device, and calibrating the sensor according to the weight indicated by the independent device.

After the zero calibration the next one will normally be one where the body is left to rest normally under its own weight. This will produce a second point for the sensor output/weight relationship curve or straight line. The body can then be loaded further to produce one or more points beyond the second one, and if desired the lifting force can be re-applied to relieve the weight so that points intermediate the zero and normal loading points can be determined.

As mentioned above, this is primarily intended for vehicles with sensors on the axles, one for each wheel between that wheel and the suspension point.

To calibrate, the body is Jacked up at different points in succession so that each wheel in turn is relieved of weight to calibrate the zero of its associated sensor. When so jacked up, a slim platform weighing device can be slid under the wheel, and as the jack is released, that device indicates the bearing weight of the wheel. This is then recorded against the sensor reading, and the table so obtained could then be provided in easy "look-up" form. Alternatively, the results could be recorded electronically and sensor outputs could then be translated into direct read-outs of weight by reference to the memory storing those results.

The accompanying drawings FIGURE 1. and 2. show, by way of example and in very diagrammatic form, two stages in the calibration process of a sensor on a vehicle axle.

Claims (3)

1. A means of calibrating an electronic weighing sensor aimed at weighing an axle vehicle involving no standard 'dead' weights.

2. A means of calibrating an electronic weighing sensor as described in Claim 1. by lifting or lowering the vehicle to be weighed such that load is removed or applied progressively and incrementally from or to the axle as described in the 'description' and FIGURES 1. and 2.

3. A means of calibrating an electronic weighing sensor as claimed in Claim 1. and 2. which can be made accurate by checking the calibration when the vehicle is later fully or significantly loaded after the initial calibration is carried out. Small adjustments to the load/voltage curve or straight line relationship can be made within the electronic readout unit to cancel any inaccurancies which might appear when this load is applied and the loaded vehicle is weighed by an accurate independent weighing machine, such as a weigh bridge. The readout unit weight indication being made identical to the accurate independent weighing machine.

indication.