GB2217884A

GB2217884A - Transducer system

Info

Publication number: GB2217884A
Application number: GB8809770A
Authority: GB
Inventors: Brian Arthur Selmes
Original assignee: Crystalate Electronics Ltd
Current assignee: Crystalate Electronics Ltd
Priority date: 1988-04-25
Filing date: 1988-04-25
Publication date: 1989-11-01
Anticipated expiration: 2008-04-25
Also published as: GB8809759D0; GB2217884B

Abstract

A system is provided for processing variable electrical signals from a plurality of strain gauge networks (1, 2, 3, 4) on a structure whereby a resultant electrical output from each network is only a function of a designated force which each network is intended to monitor and has been corrected for a reaction by the network to forces which other strain gauge networks on the structure are intended to monitor. The system includes interconnected processing means (5, 6, 7, 8) for connection to the networks (1, 2, 3, 4) whereby an electrical signal from each network is applied to an associated processing means. Each processing means (5, 6, 7, 8) has means to amplify, and optionally to invert, the signal received from its associated network (1, 2, 3, 4) and also has means incorporating selected electrical resistors (9, 10, 11, 12), to receive from the other processing means and to add to or subtract from the signal, a predetermined proportion of corresponding amplified and optionally inverted signals from the other processing means. Output means (13, 14, 15, 16) is provided for each resultant signal. <IMAGE>

Description

ACTIVE TRANSDUCER SYSTEM This invention relates to a system and method for processing variable electrical signals from a plurality of strain gauge networks on a structure.

It is a common engineering requirement to measure the forces applied to a structure in service or test conditions. These force systems may be complex but can be defined by a series of separate forces and couples. The ideal method of measuring each of these forces is to apply a series of strain gauge bridges to the structure with each one positioned to react only to one particular force. This is only possible on simple structures. In general such strain gauge bridges, whilst reacting to a designated force, will also react, to some extent, to the other applied forces. This unwanted reaction is known as mechanical cross-talk. If the component loads can be applied individually in a calibration procedure then the mechanical cross-talk can be measured.During normal operation the loads are applied in some unknown combination and it has hitherto not been possible to separate out the required bridge output from the cross-talk.

It is an object of the present invention to provide a processing system which is adapted and arranged to achieve de-coupling of the signals in such a way that the output from each combination of strain gauge network and its associated electronic circuits is substantially a function only of a designated force which the strain gauge network is intended to monitor.

The present invention provides a system for processing variable electrical signals from a plurality of strain gauge networks on a structure, said system including a plurality of interconnected processing means adapted to be electrically connected to the strain gauge networks whereby an electrical signal from each network is applied to an associated processing means, each processing means being provided with: means to amplify the electrical signal received from the network associates therewith; means optionally to invert said signal; means to supply to the other processing means a predetermined proportion of the amplified and optionally inverted signal; means to receive from the other processing means and add to or subtract from said signal the ptedetermined proportion of corresponding amplified and optionally inverted signals from the other processing means; and output means for the resultant signal.

Preferably the means to receive the predetermined proportion of said signals from the other processing means incorporates electrical resistors, the value of each resistor being selected to give precisely the required proportion of the signal from another processing means.

Each processing means may conveniently be packaged, e.g., in hybrid circuit form, and provided with terminals to which a series of the said electrical resistors can be subsequently connected after selection.

Each strain gauge network is suitably connected in Wheatstone bridge configuration.

In practice, a series of strain gauge bridges are applied to a structure under investigation at suitable locations to determine a required number of mutually independent forces. One strain gauge bridge is applied for each independent force to be measured, each strain gauge bridge being located so that it is influenced as little as possible by the other independent forces applied to the structure. The independent forces are then applied separately to the structure and the outputs determined from the bridges which are not intended to monitor the particular force being applied. These outputs provide a measure of mechanical cross-talk in the structure between the various strain gauge bridges.The cross-talk data is fed into a suitably programmed computer and used to obtain appropriate values of electrical resistors which are required to be connected to each processing means to achieve compensation in eac processir.g means for the cross-talk. w . the aDpro?rnave resistors connected and the processing means interconnected with one another on the structure and each connected to its associated strain gauge bridge, the system is then ready for use. The output from each processing means will then be substantially a function only of one designated force.

The. following example illustrates the invention, reference being made to the accompanying drawing which provides a schematic diagram of an embodiment of processing system according to the invention.

In the motor vehicle industry, vehicles are often tested on servo-hydraulic machines which are required to simulate vehicle 'in service' condltions. This method of testing requires a knowledge of 'in service' dynamic forces occurring between the vehicle and the road. The force system applied to any one wheel can be defined by four independent forces, namely Vertical, Fore/Aft, Transverse and Torque. It is impossible to introduce a series of standard transducers to measure these and so it is desirable to strain gauge the axle, through which all loads are transmitted, to measure these loads individually.Even with the best gauge positioning procedures it is not possible to eliminate cross-talk so that a strain gauge bridge network applied and intended to measure vertical forces, will also show some output when fore/aft, transverse and torque forces are applied. The accompanying drawing shows an arrangement of processing circuits designed to substantially eliminate mechanical cross-talk. For simplicity, only the interconnections for eliminating cross-talk with regard to vertical load determination are shown, but it will be readily appreciated that similar interconnections will apply for eliminating cross-talk with regard to fore/aft and transverse load determination and for torque determination.Reference numerals 1, 2, 3, 4 denote Wheatstone bridge networks of electrical resistance strain gauge elements applied to the vehicle axle to determine vertical, fore/aft, transverse and torque loads respectively on the axe. Reference numerals 5, 6, 7, 8 denote processing means associated with the strain gauge bridges 1, 2, 3, 4 respectively.

Each processing means 5, 6, 7, 8 includes an anpiifier (A4P) Z an inverter (INV), a supply voltage halving means (V/2) and a summing amplifier (SsE). V+ and V- represent a supply voltage for eac processing means. Reference numerals c, C, il, 1 denote electrical resistors which are selected during test conditions and connected to the processing means 5, 6, 7, 8 and through which correcting signals are applied to each processing means so that the outputs at terminals 13, 14, 15 and 16 of processing means 5, 6, 7, 8 respectively represent substantially true vertical, fore/aft, transverse and torque loads on the axle.

In this example, it will be noted that each processing means 5, 6, 7, 8 can accept up to seven channels of cross-talk decoupling, thus creating a maximum of eight channels. This is not a system limitation as each decoupling connector on each processing means can accept more than one input.

Claims

1A system for processing variable electrical signals from a plurality of strain gauge networks on a structure, said system including a plurality of interconnected processing means adapted to be electrically connected to the strain gauge networks whereby an electrical signal from each network is applied to an associated processing means, each processing means being provided with: means to amplify the electrical signal received from the network associated therewith; means optionally to invert said signal; means to supply to the other processing means a predetermined proportion of the amplified and optionally inverted signal; means to receive from the other processing means and add to or subtract from said signal the predetermined proportion of corresponding amplified and optionally inverted signals from the other processing means; and output means for the resultant signal.

2 A system according to Claim 1 in which the means to receive the predetermined proportion of said signals from the other processing means incorporates electrical resistors, the value of each resistor being selected to give precisely the required proportion of the signal from another processing means.

3 A system according to Claim 1 or 2 in which each processing means is packaged and provided with terminals to which a series of the said electrical resistors can be subsequently connected after selection.

4 A system according to Claim 1, 2 or 3 in which each strain gauge network is connected in Wheatstone bridge configuration.

5 A system for processing variable electrical signals constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.