SU964476A2 - Strain-gauge weight measuring device - Google Patents

Description

(5) TENSOMETRIC WEIGHT MEASURING DEVICE

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This invention relates to a weight measuring technique.

BY MAIN auth. St. No. 581386, a measuring device is known, comprising a pulse generator with a time setting RC circuit, a matching unit, a bridge parametric converter and a matching amplifier l.

A disadvantage of the known device is the comparatively low measurement measurement / due to the nonlinearity of the bridge, parametric converter.

The aim of the invention is to increase the measurement accuracy.

The goal is achieved by inserting a potentiometer included in the measuring diagonal of the bridge, and an additional amplifier, through which the top of the diagonal of the bridge power supply is switched to the front bus, with the first input of the additional amplifier turned on

on the movable contact of the potentiometer, and the second is connected to a common bus.

In this case, an additional amplification stage, through which the potentiometer is turned on, into the bridge diagonal, can be introduced into the device.

FIG. 1 and 2 are presented to the scheme. | We offer the device (options).

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The tensometric weighing device contains a generator of 1 pulses with a time specifying an RC circuit, a matching unit 2, a bridge parametric converter 3

15 matching amplifier k, potentiometer 5, additional amplifier 6, gain stage 7.

The device works as follows.

20

Claims (2)

The output signal of a bridge parametric converter 3 (connecting, for example, from strain gauges assembled according to a bridge circuit on an elastic element by force measuring its date), amplified by matching amplifier k, is applied to the capacitance of the KS circuit i, which leads to a change in the generation period T (equal to t in the case of a zero output signal of the bridge converter with the balance of the latter). The generation period T is linearly related to the magnitude of the span of the bridge of the parametric converter 3, i.e. directly proportional to the coefficient (M1 to the transfer of K d to the bridge converter. The magnitude of Kuu is determined by the relative change of Sc by the resistance R of the strain gauges under the influence of the force K hC –M. C ″ - R. At the nonlinear character of the transfer coefficient of the bridge 3 about its input the magnitude (force) period is nonlinearly related to the magnitude of the force. Potentiometer 5 and additional amplifier 6 allow the bridge parametric converter 3 to be supplied with voltage depending on its balance level. Thus, the transmission coefficient of the parametric motor The new converter 3 becomes non-linearly related to the value of the resistance of the strain gauge in its shoulders 14 The magnitude and sign of this non-linearity are uniquely associated with the position of the potentiometer slider 5. By changing the position of the potentiometer slider 5, compensation can be obtained for the original non-linearity of the 3 ”bridge parametric converter. ka potentiometer 5 (1), Fig. 1) when we receivefp 0, i.e. vp, vtf 2k (1) -B. The transmission coefficient of bridge 3 is defined as. „,. K -: (2) ll Cf U / With a relative change in the resistance of the resistance strain gages taking into account (1) the expression (2). has the form 1 i (2UN) Having decomposed (3) in a row and neglects us, of course, above the first (so typical value), we have) () Taking into account that in the usual scheme without correction of nonlinearity. we obtain (-2) 3 From the formula (s) it follows that the nonlinearity of the bridge parametric converter is compensated for in the P | 4e case of the maximum ratio I (& Rlt) of the transform; paddle corresponding to the rated load. If for semiconductor-: cubic strain gages with URIR) of this degree of compensation (11) is in most cases sufficient, then for bridges made of metal strain gauges with (DH | I) - 2-10 the depth of combination is small (+ 0.2%). TOI most strain gauges with such bridges are available in accuracy classes of 0.25-0.6. In order to increase the degree of compensation for nonlinearity, in this case an amplification cascade is introduced, for example, according to the known scheme of a potentiometric amplifier (Fig. 2). Parallel to the output of this cascade, a potentiometer 5 is connected, the slider of which is connected to the inverting input of an additional amplifier 6. The difference from this scheme is that the compensating signal is amplified by a gain cascade in, where Cd is the gain factor of the cascade for the differential signal. The degree of nonlinearity composition in this device is determined by the | Formulas l and is amplified by a factor of K times in comparison with the scheme shown in FIG. The use of 1 will allow the use of less accurate strain gauges in those cases where previously it was possible to use only precision (and, therefore, more expensive) strain gauges ... Claim 1. Strain gage weighing device according to ed. St. H 581386, characterized in that, in order to improve the measurement accuracy, a potentiometer included in the measuring diagonal of the bridge and an additional amplifier are inserted into it, through which the top of the diagonal of the bridge power supply is connected to the common bus, and the first input of the additional amplifier is connected to the moving contact potentiometer, and the second is connected to a common bus. 2. The device according to claim 1, that is, 10 with the fact that the E 64 introduces an amplification stage through which the potentiometer is inserted into the measuring diagonal of the bridge. Sources of information taken into account during the examination 1. USSR Author's Certificate No. 581386, cl. G 01 G 23/36, 06.02.76 (prototype). ag.1