Wheatstone bridge output

In its simplest form, the Wheatstone bridge is used on D.C. for the measurement of an unknown resistance in terms of three known resistors. Its accuracy depends on that of the known units and the sensitivity of the detector. It is also used for sensing the changes which occur in the output from resistance strain-gauge detectors. The latter instruments can be made portable and can detect variations of less than 0.05 per cent. 

The actual design includes a second filament, within the same detector block. This filament is present in a different flow channel, however, one through which only pure helium flows. Both filaments are part of a Wheatstone Bridge circuit as shown in Figure 12.11, which allows a comparison between the two resistances and a voltage output to the data system, as shown. Such a design is intended to minimize effects of flow rate, pressure, and line voltage variations. 

When a flammable gas enters a catalytic cell, the gases are combusted on the active filament, causing an increase in temperature and a change in the balance of the Wheatstone bridge. The output signal for flammable gases in air in this type of cell is linear up to the lower explosive limit (LEL). 

Fig. 9b. A Wheatstone bridge circuit as used in power plants for C02. It operates by balancing the output voltage of two circuits, one in a reference gas concentration, and the other in the gas to be measured.

The Electrical Conductivity System consists of a frequency generator (the frequency is usually between 1,000 and 5,000 Hz) that provides an AC potential across the cell. As already discussed, an AC potential must be used to avoid electrode polarization. The sensor is usually placed in one arm of a Wheatstone bridge as shown in figure 3. The out-of-balance signal is then rectified with a precision rectifier and the DC signal either passed to nonlinear amplifier or a computer data acquisition system. The non- linear amplifier modifies the signal so that the output is linearly related to ion concentration. Alternatively, if the output from the precision rectifier is passed directly to the... 

A thermistor, heated by an appropriate current, is situated in the mobile phase close to the end of the column. The thermistor is situated in one arm of a Wheatstone bridge. When equilibrium has been established, the bead reaches a constant temperature where the heat lost to the mobile phase is equal to the heat ohmically generated in the bead. As a consequence, the resistance of the bead is also constant and the output of the bridge can be balanced to zero. In the presence of a solute, the thermal equilibrium is destroyed and the heat lost from the bead changes as a result of either a change in specific heat or a change in the thermal conductivity of the mobile phase. Thus, the temperature... 

The output of the Wheatstone bridge is normally expressed in millivolts per volt of excitation per unit of applied force. For example, sensitivity of 0.2 mV/ V/kN means that applying, say, lOkN force and 10 V excitation will produce 20 mV output. To utilize such output, it usually needs to be amplified several hundred times to reach units of volts. 

The temperature was measured at the top of the column with a thermistor (10 kQ at 25 °C, 1.5 x 6 mm, or equivalent) epoxied at the tip of a 2 mm (OD) acid-proof steel tube. The temperature was measured as an unbalance signal of a sensitive Wheatstone bridge. At the most sensitive setting, the recorder output produced 100 mV at a temperature change of 0.01 °C. Placing the temperature probe at the very top of the column, rather than in the effluent outside the column, reduced the turbulence around the thermistor and gave a more stable temperature recording. 

The two thermistors on which the solution droplet and the solvent droplet are placed are arranged in an Wheatstone bridge circuit in such a way that the temperature rise can be measured very accurately as a function of the bridge imbalance output voltage, AV. The operating equation is... 

The sensor s transducer principle combines a membrane, as a mechanical transducer, with thin-film metal resistors forming a Wheatstone bridge, as an electromechanical transducer. The output voltage of the Wheatstone bridge is given by... 

Fig. 5.4.10 Schematic view of four resistors in a Wheatstone bridge configuration V is the applied voltage and AV is the output signal V...

---