GB2195775A - Inclinometer - Google Patents

Abstract

An inclinometer of the kind for fitment for example to tractors, load lifting cranes, and lifting devices and gantries. So that its accuracy will not significantly fall off even after long periods of use without servicing, the inclinometer includes at least one signaling device constituted by a flexible metal strip 16 firmly anchored at one (upper) end and carrying in a region intermediate its ends at least one electrical strain gauge 20, the latter forming part of a Wheatstone Bridge electric circuit so that tilting of the inclinometer causes movement of an ammeter needle. As shown there is a pair of devices 12, 14 to measure inclination in perpendicular planes. Each strip 16 carries a pair of weights 18 at its lower end, and two strain gauges 20 connected in adjacent arms of a bridge circuit. <IMAGE>

Description

SPECIFICATION Inclinometer The invention relates to inclinometers, that is to say to devices for indicating the angle of inclination of a body towards a position from which it will overturn.

Items of apparatus to which an inclinometer may be fitted include tractors, load lifting cranes and lifting devices and gantries by means of which access can be had to street lamps and the like.

Various constructions of inclinometer have previously been used but these have usually included a pendulum device mounted in such a way that it can swing freely with very little friction. However, in practice, any pivot has friction and the small amount of friction present in the pivots of previously known inclinometers has been found to be significant so that errors in the readings have been caused, particularly after long use of the inclinometer and perhaps when it has been in need of servicing.

The object of the invention is to provide a construction of inclinometer in which errors of this sort will not be a problem even after long periods of use without servicing.

According to the invention, there is provided an inclinometer including at least one signalling device constituted by a flexible metal strip firmly anchored at one end and carrying in a region intermediate its ends at least one electrical strain gauge, the electrical strain gauge forming part of a Wheatstone Bridge electric circuit so that any variation in the electrical resistance of the strain gauge, as a result of flexing of the flexible metal strip in response to tilting of that part of the inclinometer to which the one end of the flexible metal strip is firmly anchored, causes a movement of an ammeter needle, the ammeter being appropriately calibrated to indicate the degree of tilting. Preferably, the or each flexible metal strip will carry respective strain gauges on its opposite sides, the two electrical strain gauges both forming part of the Wheatstone Bridge electric circuit.Preferably, also, the or each flexible metal strip will carry a weight at its free end, that is to say its end remote from its firmly anchored end, the weight preferably being constituted by a pair of weight elements of equal mass secured on opposite sides of the metal strip. The inclinometer will preferably include a pair of signalling devices as described above, the signalling devices being located in mutually perpendicular planes.

In order that the invention may be fully understood and readily carried into effect, an embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a perspective view, partly in section, of an inclinometer embodying the invention, and Figure 2 is an electrical circuit diagram.

Referring now to Figure 1 of the drawings, the inclinometer there illustrated is housed in a substantial metal block generally indicated 10 and includes a pair of signalling devices 12 and 19 located in mutually perpendicular planes. Each signalling device is constituted by a flexible metal strip 16 firmly anchored at one end within the metal block and carrying at its other end a weight (the weight being constituted by a pair of weight elements 18,18 respectively secured on opposite sides of the metal strip) and by a pair of electrical strain gauges 20,20 respectively secured on opposite sides of an intermediate length of the metal strip. The arrangement is such that when the metal block is placed on a perfectly level surface, both signalling devices hang straight down so that the electrical strain gauges are perfectly matched.However, when the block is caused to incline one way or the other, one or the other of the flexible metal strips is caused to flex very slightly with the result that the electrical resistances of the electrical strain gauges secured on its opposite sides are caused to vary to an extent proportional to the angle of inclination of the block.

Referring now to Figure 2, the electrical strain gauges 20,20 of one of the flexible metal strips represent the two resistances on one side of the Wheatstone Bridge circuit there illustrated, the other two resistances R1 and R2 being reference resistances. An electric current is passed through the circuit, as shown, and any imbalance between the electrical resistances of the strain gauges 20,20 resulting from the flexing of the flexible metal strip concerned, is shown as a negative or positive reading on an ammeter 22, the latter being calibrated in degrees of inclination.It will be understood that for the inclinometer illustrated in Figure 1, that is to say having a pair of signalling devices, the electrical circuit just described will be duplicated, respective ammeters, calibrated in degrees of inclination, being provided to indicate inclinations in the two mutually perpendicular planes.

It has been found that the inclinometer just described operates very accurately and it can be expected to do so virtually indefinitely because of the fact that it is devoid of pivots which might have significant frictional resistance to movement after long use. However, various modifictions may be made. For example, if it is required to measure inclinations in only one plane the inclinometer can have but a single signalling device as described, and of course a single electric circuit as described and including an ammeter suitably calibrated in degrees of inclination. It will be understood that although the or each ammeter will preferably be calibrated in degrees of inclination this need not necessarily be the case.For example, in the case of an inclinometer fitted to an item of apparatus such as a tractor, the dial of the ammeter could be marked with differently coloured sectors, for example a green sector representing a safe working condition and respective red sectors at opposite sides of the green sector, the red sectors representing unsafe working conditions, that is to say dangerous inclinations from which overturning is likely to take place.

In the illustrated embodiment the respective ammeters which constitute the dials are shown to be contained in a box separate from the -substantial metal block in which the pair of signalling devices are located, the connections from the electrical strain gauages of the -signalling devices to the electric circuits within the box being by way of a cable. However, it will be understood that the substantial metal block could be made larger for the ammeters constituting the dials to be located in it. In addition, if the at least one flexible metal strip was of sufficient length to flex under its own weight, the separate weights at its free end would not be required. The inclinometer could be made to work if the or each flexible metal strip had only a single electrical strain gauge secured to it on one side, the strain gauge omitted from the Wheatstone Bridge electric circuit concerned being replaced buy a further reference resistance, but the inclinometer would probably be of reduced accuracy.

Claims (6)

1. An inclinometer including at least one signalling device constituted by a flexible metal strip firmly anchored at one end and carrying in a region intermediate its ends at least one electrical strain gauge, the electrical strain gauge forming part of a Wheatstone Bridge electric circuit so that any variation in the electrical resistance of the strain gauge, as a result of flexing of the flexible metal strip in response to tilting of that part of the inclinometer to which the one end of the flexible metal strip is firmly anchored, causes a movement of an ammeter needle, the ammeter being appropriately calibrated to indicate the degree of tilting.

2. An inclinometer according to claim 1, in which the- or each flexible metal strip carries respective strain gauges on its opposite sides, the two electrical strain gauges both forming part of the Wheatstone Bridge electric circuit.

3. An inclinometer according to either one of the preceding claims, in which the or each flexible metal strip carries a weight at its free end, that is to say at its end remote from its firmly anchored end.

4. An inclinometer according to claim 3, in which the weight caried by the or each metal strip is constituted by a pair of weight elements of equal mass secured on opposite sides of the metal strip.

5. An inclinometer according to any one of the preceding claims, including a pair of said signalling devices, the signalling devices being located in mutually perpendicular planes.

6. An inclinometer constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.