Differences Between Relay Control and Sequence Control

Relay Control

- Only on/off control can be performed.

- The frequency of failure or breakdown is high and maintenance is not easy.

- Circuits are modified by changing wiring.

- For large-scale systems, large space and long design period are required.

- Identifying the cause of a failure or an error and replacing the failed device are not easy.

Sequence Control

- On/off control and complex control can be performed.

- Reliability is high and maintenance is easy.

- Circuits are flexibly modified by using programs.

- Even for large-scale systems, large space and long design period are not required, offering flexibility and extendibility.

- All failures and errors can be monitored. The failed device can be replaced easily.

Reference : Mitsubishi's FA E-Learning

Comments

Example of PLC ladder diagram for Filing and Heating Liquid in Tank

In the previous post, I wrote PLC program about Mixing and Heating process. Today, I'm going to write about Filling and Heating process in tank. It sounds like the same topic in previous post. Actually, it is different. We'll see the sequences and processes. Here is the given sequences according to the Author : 1. Fill the tank up to 80%. When the tank is filled, turn ON the heater to raise the temperature up to 70 deg. 2. When this temperature is reached, turn OFF the heater & open the outlet valve. 3. When the level in the tank falls below 10%, close the output valve. In this situation, I do the ladder diagram via Sysmac Studio which is the product of Omron. I just remind you again, most of the control processes are used with Mitsubishi, Siemen and sometimes Delta's PLC due to cost effectively. I'm going to show you how it works with Sysmac Studio. In this case, I'm only using Name Tags. Before I'm talking about ladder diagram, I would like to tell about ...

4-20mA Formulas

As seen in the accompanying image, the voltage output of a 4–20 mA transmitter can be transformed to a specific range, from 0 to a maximal amplitude Vmax: I [mA] = ( ( (V − Vmin) / ( Vmax − Vmin) ) × 16 ) + 4 (Voltage to Current) V [Voltage] = ( (I − 4 ) / 16) × ( Vmax − Vmin ) + Vmin (Current to Voltage) PV [units] = ( (I − 4 ) / 16) × ( PVmax − PVmin ) + PVmin (Current to Process Variable) Where, I is the current. V is the voltage. PV is the Process Variable. min is the Lower Range Value of the respective signal. max is the Upper Range Value of the respective signal. Keep in mind that the min and max values and units must match. For Voltage to Current, As an illustration, The output voltage of an analog output card is 3V, and its total range is 0–6V. Determine the corresponding 4–20 mA current value. I = ( ( (V − Vmin) / ( Vmax − Vmin) ) × 16 ) + 4 I = ( ( (3 − 0) / ( 6 − 0) ) × 16 ) + 4 I = 12A Reference : Instrumentationtools

What is Master Control Relay in PLC?

A PLC's Master Control Relay (MCR) is defined by experts as a unique relay utilized in ladder logic programming to regulate the operation of several rungs or parts of a ladder diagram. In essence, it uses certain conditions to determine whether to enable or disable particular software sections. All rungs between the MCR and the associated end instruction are executed when the MCR is turned on. These rungs cannot run if the MCR is deactivated because they are circumvented. Large portions of a program can be controlled with a single condition because to this functionality, which enhances program organization and efficiency. In first photo, Master Control Relay is used as normally opened coil, called Master Coil. As you can see when the "Start" is triggered, Master Coil will be closed contact and executes the multiple rungs. If "Stop" is triggered, Master Coil is disable the execution of the other rungs. Similarly, in second figure, I...

All About Automation, Control System and Management

Search This Blog