Category: Mechatronics, Industrial Control & Instrumentation
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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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Toggle Switches
Toggle switches are available in various contact configurations. Each switch consists of one or more poles, where each pole is actually a separate switch. The switch contact configurations include: Single-pole/single-throw switch (SPST) This is the simplest switch. It has a single set of contacts that can either open or close. Its contact configuration is illustrated…
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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…
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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: In flow measurement the vortex shedding frequency is usually a few hundred hertz (Hz). At Reynolds numbers over 103 the volumetric flowrate, Q, is directly proportional to the observed…
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The Principle of an Optical Pyrometer Temperature Sensor
A heated object emits electromagnetic radiation. At temperatures below approximately 400 °C this radiation can be felt as heat. As the temperature rises, the object starts to emit visible radiation passing from red through yellow to white. Intuitively we can use this radiation to qualitatively measure temperature as illustrated in the table below: Temperature Colour…
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Types of Ultrasonic Non-Destructive Testing (NDT) Techniques
The technology of ultrasonic testing has been used by production and industry since the development of the radio engineering process. The effect and device of the technology are that ultrasonic waves of acoustic type do not change the rectilinear trajectory of motion when passing through a homogeneous medium. The ultrasonic method is also used to…
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The Principle of Operation of Optical Encoders
An encoder is a device that provides a digital output as a result of an angular or linear displacement. The position encoders can be grouped into two categories: Incremental Encoders Let’s consider the basic form of an incremental encoder for the measurement of angular displacement of shaft shown below: The incremental encoder shown above consists…
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Features of Analog Signal Transmission
Analog voltage or current signals are hardwired between the transmitter and the receiver. These analog signals can be relatively be slow to settle compared to digital signals, due time constant of the lead capacitance, inductance and resistance. Analog signals can lose accuracy if the signal lines are long with high resistance. These signals can be…