Design a Temperature Indicator

This circuit is a temperature indicator circuit or differential instrumentation amplifier using a transducer bridge. This circuit is calibrate in degrees Celsius or Fahrenheit. In the circuit used buffer in  and  points for exact voltage of  and  points. Because gain is always 1 of buffer circuit. Then the output voltage of buffers is input voltage of differential amplifier. 

The differential amplifier is difference voltage of  and  points using 741 Op Amp. When temperature is increased then resistance  is also decreased and output voltage  is decreases and when temperature is decreased then resistance  is also increased and output voltage  is increases.

The temperature indicator is a circuit that indicates of temperature in degrees Celsius or Fahrenheit. The temperature is inversely proportional to the resistance or transducer.

  The Fig.01 simplified a temperature indicator circuit using a transducer bridge. A restive transducer whose resistance changes as a function of some physical energy or temperature is connected in one arm of the bridge with a small circle around it and is denoted by , where  is the resistance of the transducer and  is the change in resistance.

Fig.01 - Temperature indicator

In the circuit used as the transducer in the bridge circuit is a thermistor and replaced output voltmeter to temperature indicating meter. Then temperature indicating meter is calibrate in degrees Celsius or Fahrenheit. 

The bridge can be balanced at a desired reference condition, for instance 25⁰C. As the temperature varies from its reference value, the resistance of the thermistor changes and the bridge become unbalanced. This unbalance bridge in turn produces the meter movement.

Analog weight Scale

The most common weight-scale implementation is to use a  transducer bridge, with voltage output directly proportional to the weight placed on it. The trend in weight scales towards higher accuracy and lower cost has produced an increased demand for high-performance analog signal processing at low cost.By connecting a strain Gage in the bridge ,the differential instrumentation amplifier can be converted in to a simple analog weight scale.

 In the analog weight scale, strain Gage elements are connected in all four arms of the bridge. The elements are mounted on the base of the weight platform, so that, when an external force or weight is applied to the platform, one pair of elements in the opposite arms elongates, whereas the other pair of elements in the opposite arms compresses.

 On the other hand, When no weight is placed on the platform, the bridge is unbalanced, R_T1=R_T2=R_T3=R_T4=R, and the output voltage of the weight scale can be zero. When a weight is placed on the scale platform, the bridge becomes unbalanced. In other words, when the weight is placed on the platform, R_T1 and R_T3 both decrease in resistance and R_T2 and R_T4 both increase in resistance (Figure 01).

 

The analog weighing measuring scales need to be hung properly before we start measuring anything using the same. They never allow measuring the weight of anything that we want as they have some limitations. If we think about measuring anything using an analog scale we need to check the analog lines to get the nearby accurate measurement.


One thing we need to keep in our mind while using such a scale is the limitation, if we load anything which weights more than the mentioned limit by the manufacturer of the scale we may end up damaging the same. Analog scales were never capable of providing accurate weight of any item and at the same time, it involves human effort to measure anything where the chances of human error are quite normal

For better accuracy, a microprocessor-based digital weight scale may be constructed.But it is much more complex and expensive than the analog scale.