Author: John Mulindi
-
The Shockley Diode Features & Operation
The Shockey diode is a four layer sandwich of PNPN semiconductor material very similar to the SCR but without a gate as illustrated in the Figure 1.0 below: The Operation of Shockley Diode A Shockley diode can be turned ON by applying enough voltage between anode and cathode. This voltage will cause one of the…
-
Basic Features of Autotransformer Starter
A 3-phase autotransformer is typically employed where star or delta starting provides insufficient starting torque. Each phase of an autotransformer consists of a single winding on a laminated core. This incoming supply is connected across the ends of the coils, and one or more tapping points (or a sliding contact) provide a reduced voltage output…
-
Manipulating Devices & Actuators in Process Instrumentation
The function of the manipulating device is to influence the process variable. Its main purpose is to regulate a mass or energy flow. Mass flows can be either in gaseous or liquid state e.g. steam, natural gas, fuel oil, etc. The energy flows typically take the form of electrical energy. The energy supply can be…
-
The Diac Features & Applications
Features of a Diac The diac is a two-terminal, semiconductor, bi-directional switching device. It can conduct in both directions. The diac closely resembles a PNP transistor without an external base terminal. Operation of a Diac The diac does not conduct except for a small leakage current) until the breakover voltage VS is reached, typically 20…
-
ZigBee Wireless Protocol for Industrial Communication
ZigBee is an open wireless standard for low-rate networks. It is an IEEE standard 802.15.4 protocol. The physical layer radio operates at 2.4 GHz band carrier frequencies with direct sequence spread spectrum (DSSS). It supports a range of up to 70 m. Data transfer rate supported is 250 kbps. It supports sixteen channels. A ZigBee…
-
Unijunction Transistor Features and Operation
The unijunction transistor (UJT) is a three terminal, single-junction device which exhibits negative resistance and switching characteristics totally unlike those of conventional bipolar transistors. The UJT consists of a bar of n-type having ohmic contacts designated Base 1 (B1) and Base 2 (B2) on either side of a single PN junction designated the emitter. An…
-
What is a Discontinuous Controller?
This is a controller with only 2 switching states, that is, the output signal is switched ON and OFF depending on whether the process variable goes below or above a preset limit or setpoint. An example of a discontinuous controller is a resistance thermometer (Pt 100), whose electronic circuitry switches heating on if the temperature…
-
How Modbus is used in Industrial Networks
Modbus is an open standardized communication protocol that was founded by Modicon. Initially it was designed for the communication among PLCs in industrial applications but it also gained significance use in building automation domain for instance in HVAC systems, DDCs and room control. In a nutshell, Modbus is an application layer messaging, protocol placed at…
-
Network Access Control Techniques
Access control methods are required in a network to ensure that only one user of the network is able to transmit at any one time. In ring-based local area networks (LANs), two commonly employed techniques are: Token Passing In this technique, a token i.e. a special bit pattern, is circulated. When a station wishes to…
-
Types of AC Motors
Classification of AC Motors The AC motors works by rotating the stator field, they make use of the natural alternating nature of the AC wave to turn the field coils on and off sequentially. Generally, AC motors can be classified into two groups: single-phase and polyphase, with each group being further subdivided into induction and…