Tag: instrumentation
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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 … Read more
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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 … Read more
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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. Figure: DC Ammeter Calibration An ammeter may be calibrated by comparing it to a more accurate (standard) ammeter measuring the same … Read more
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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 … Read more
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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: Figure: Flow control system In the system above, the controller’s function is to maintain the flow of a liquid … Read more
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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: Figure: Electric solenoid actuator The coil is connected to an external current supply. The spring rests on the armature to … Read more
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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 … Read more
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Key Factors to Consider in Selection of Valves
Valves are the final element in a control loop, and are critical in providing the correct flow. The valve, usually operates in very harsh conditions, and is one of the most costly elements in the process control system. Their … Read more
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Features and Applications of Instrument Transformers
Instrument transformers are used in the measurement of voltage, current, energy, and power in ac circuits. The main reasons why instrument transformers are employed in measurements are: To extend (multiply) the range of the measuring instrument. To isolate the measuring … Read more
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The Principle of Operation of a Vortex Flowmeter
If a bluff (non-streamlined) body is placed in a flow, vortices detach themselves at regular intervals from the downstream side as illustrated in the diagram below: Figure: Vortex shedding flowmeter In flow measurement the vortex shedding frequency is usually a … Read more