Auto-zeroing-scale

Electronic scales have become widely used, and the HA-510X, recognized for its very low noise characteristics, can enhance such designs. This circuit incorporates a strain gauge sensing element as part of a resistive Wien bridge. An auto-zero circuit is integrated into the design by including a sample-and-hold network. The bridge signal is fed into the inverting input of a differentially configured HA-5102. The non-inverting input is connected to the other half of the HA-5102, which acts as a buffer for the holding capacitor, CH. This second amplifier and its capacitor CH create the sampling circuit used for automatic output zeroing. A 20-kΩ resistor between the holding capacitor CH and the input terminal minimizes the drain from the bias currents. A second resistor, RG, is included in the feedback loop to counterbalance the effect of R8. If R7 is approximately equal to the resistance of the strain gauge, the input signal from the bridge can be roughly nulled with R6. With precise matching of the ratio R4/R1 to R3/R2, the output offset can be adjusted to zero by closing switch S1. This action charges CH and results in a 0-V difference at the inputs of the second amplifier, leading to a 0-V output. Consequently, the output of the strain gauge can be effectively zeroed. Resistor R10 and potentiometer R11 offer an additional means for fine-tuning V_out, although they may also increase the offset voltage away from the zero point. Capacitors C1 and C2 are employed to reduce the circuit's susceptibility to noise and transients.

The HA-510X electronic scale circuit is designed to provide precise weight measurements while minimizing noise interference. The use of a strain gauge as the sensing element is critical, as it converts mechanical strain into a change in resistance, which is then processed by the Wien bridge configuration. This configuration is particularly effective for ensuring stability and accuracy in low-noise applications.

The integration of the sample-and-hold network serves to maintain a stable output during measurement, allowing for the automatic zeroing of the output signal. The differential amplifier configuration of the HA-5102 is essential for amplifying the small signals generated by the strain gauge while rejecting common-mode noise, which is prevalent in electronic measurements.

The choice of resistors R7, R6, R4, R1, R3, and R2 is crucial for achieving the desired balance and nulling of the output signal. The careful selection and matching of these resistors ensure that variations in the strain gauge resistance do not adversely affect the output readings. The 20-kΩ resistor is strategically placed to limit the bias current drain, thereby enhancing the circuit's overall performance.

The operation of switch S1 allows for the adjustment of the output offset to zero, which is vital for accurate measurements. This feature is particularly useful in applications where the scale may need to be calibrated frequently or where environmental factors could affect the baseline readings.

Finally, the inclusion of capacitors C1 and C2 enhances the circuit's robustness against noise and transient signals, ensuring that the output remains stable even in electrically noisy environments. This design approach results in a highly reliable and accurate electronic scale that meets the demands of various industrial and commercial applications.Electronic scales have come into wide use and the HA-510X, as a very low noise device, can improve such designs. This circuit uses a staingauge sensing element as part of a resistive Wienbridge. An auto-zero circuit is also incorporated into this design by including a sample-and-hold network. The bridge signal drives the inverting input of a differentially configured HA-5102. The noninverting input is driven by the other half of the HA-5102 used as a buffer for the holding capacitor, CH.

This second amplifier and its capacitor CH form the sampling circuit used for automatic output zeroing. The 20-KO resistor between the holding capacitor CHand the input terminal, reduces the drain from the bias currents.

A second resistor RG is used in the feedback loop to balance the effect of R8. If R7 is approximately equal to the resistance of the strain gauge, the input signal from the bridge can be roughly nulled with R6. With very close matching of the ratio R4/Rl i:o R3/R2, the output offset can be nulled by closing Sl.

This will charge CH and provide a 0-V difference to the inputs of the second amplifier, which results in a 0-V output. In this manner, the output of the strain gauge can be indirectly zeroed. RIO and potentiometer Rll provide an additional mechanism for fine tuning VouT. but they can also increase offset voltage away from the zero point. Cl and C2 reduce the circuit"s susceptibility to noise and transients. 🔗 External reference