Tag: instrumentation
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Null vs. Deflection Type Instruments
Null Instrument The null technique is one of the operational modes for a measuring instrument. A null instrument employs the null method for measurement. In this technique, the instrument exerts an influence on the measured system so as to oppose the effect of the measurand. The influence and the measurand are balanced until they are…
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Analog vs. Digital Sensors
Analog Sensors Analog sensors provide a signal that is continuous in both its magnitude and its temporal (time) or spatial (space) content. Most physical variables such as, current, pressure, temperature, displacement, acceleration, speed, light intensity and strain tend to be continuous in nature and are readily measured by an analog sensor and represented by an…
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Basic Features of a DC Potentiometer
A potentiometer is an instrument that is used for measurement of potential difference across a known resistance or between two terminals of a circuit or network of known characteristics. A potentiometer is also used for comparing the emf of two cells. A potentiometer is widely used in measurements where the precision required is higher than…
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Variable Capacitance Sensors
Several mechanical input sensors, as well as some sensors which measure humidity or temperature, operate by the transduced quantity causing a change in capacitance, which in turn, is converted to an analog output voltage by an ac bridge circuit or other electronic system. The capacitive sensors have been designed to measure force by means of…
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How to calibrate a dc voltmeter
An instrument may be calibrated by comparing its reading with that of a more accurate instrument when both are measuring the same quantity. The more accurate instrument is used as a standard for comparison purposes. The figure below illustrates the method for calibrating a dc voltmeter. An appropriate dc voltage level is applied from the…
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How to calibrate a dc ammeter
The figure below shows two dc ammeters connected in series, so that they are both measuring the same current. An ammeter may be calibrated by comparing it to a more accurate (standard) ammeter measuring the same quantity. The accuracy of the standard instrument should be at least four times better than the instrument to be…
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What are PLC-Based Water Treatment Plants?
Most of the water treatment plants in the previous decade were manually operated. However, they were automated to a certain degree using relays or electrical control panels but the system was not reliable and required a lot of space. In this modern era, water treatment facilities are automatically operated using PLC or Programmable Logic Controllers…
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Analog Proportional Controller
An analog controller typically employs op-amps to provide the necessary gain and signal processing. Let’s consider the flow control system below: In the system above, the controller’s function is to maintain the flow of a liquid through a pipe at 6 gallons/minute. This system consists of: The flow valve is operated with a signal…
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Electric Solenoid Actuator – Features & Operation
A typical electric solenoid actuator consists of a coil, armature, spring, and stem. This is illustrated in the figure below: The coil is connected to an external current supply. The spring rests on the armature to force it downward. The armature moves vertically inside the coil and transmits its motion through the stem to the…
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Pressure Control Valve Operation
A pressure control valve is a spring-loaded valve that is capable of maintaining a constant pressure in a system regardless of the flow rate. This is important, since most pumps e.g. gear pumps are constant-displacement types – a constant volume of fluid is pumped for each revolution of the pump shaft. If the pump were…