Why is RTO used in the Place of TON Timer?

Why is RTO used in the place of T-ON?

Timers are one of the most used instructions in a PLC program.

To get started with the topic we need to know why the timers are used in the first place.

Timers are used to keep a set of outputs ON/OFF for the specified amount of time.

For example, I had to run a heater for 15 seconds I would go for a timer to make it happen.

So there are two types of an ON delay timer in RSlogix 500,

T-ON – TImer On delay timer.
RTO – Retentive TImer.

Now consider an application we are programming requires a heater to be turned on for 15 seconds after a level sensor has sensed the level is high enough.

Now we’re gonna write the logic for that using a TON.

Now we completed our logic,

I:0.0/0 – It is the sensor input address
o:0.0/0- It is the output for the heater.
T4:0/TT – It is called the timer timing bit.

The following are the specifics on Timer block,

Timer – The timer address has to be specified here.
Time Base – The time base is the one that determines how the timer runs whether for milliseconds or microseconds or seconds. It basically multiplies with the preset value. I have mentioned here 1.0
Preset – Here is where one should specify the time the timer has to be active. So (1.0*15 = 15 seconds)

Accumulator – Here is where you can see the value of the seconds the timer has run so far.

When we go to run-time you can see that our process is working fine.

The logic is working fine until when there is an emergency shut down or power shut down in a plant. Imagine that the PLC had to turn OFF.

Then we had to turn ON again after few minutes. Now the process had to repeat where it left of meaning from 4th second the timer has to start running. But it won’t work like that once there is a shut down in a PLC system the timer had to reset on its own.

You can see the above figure for understanding.

Now to overcome this situation we’re gonna use an RTO timer to develop the logic.

There is no difference in creating the instruction between TON and RTO, except we have to use a Reset here to reset the timer.

So now everything is working fine and the PLC system goes off.

You can see in the above image that the accumulator value is getting stored even after the PLC goes OFF.

So now when the system is turned ON again the program will be executed from where it left off the timer will run from 5th second as you can see below.

Even when the sensor goes OFF the timer will store the accumulator value till it ran.

Until the timer is being reset the accumulator value stays. Once it is reset the accumulator value becomes zero.

Note that the input to reset should always act like a push button or One-shot (ONS) and both the input to the timer and the input to the Reset shouldn’t be On at the same time.

This is the reason why RTO is used mostly in real-time applications.

END

Comments

PLC Program for Mixing Tank

Create a ladder diagram for controlling a batch mixing process. Implement a PLC program for mixing tank or Mixing Process using PLC Ladder Logic. PLC Program for Mixing Tank Fig : Mixing tank A tank is used to mix two liquids. The required control circuit operates as follows: A. When the START button is pressed, solenoids A and B energize. This permits the two liquids to begin ﬁlling the tank. B. When the tank is ﬁlled, the ﬂoat switch trips. This de-energizes solenoids A and B and starts the motor used to mix the liquids together. C. The motor is permitted to run for 1 minute. After 1 minute has elapsed, the motor turns off and solenoid C energizes to drain the tank. D. When the tank is empty, the ﬂoat switch de- energizes solenoid C. E. A STOP button can be used to stop the process at any point. F. If the motor becomes overloaded, the action of the entire circuit will stop. G. Once the circuit has been energized, it will continue to operate until it is manually stopped. Solution : A

What is Relay? How it Works? Types, Applications, Testing

We use relays for a wide range of applications such as home automation, cars and bikes (automobiles), industrial applications, DIY Projects, test and measurement equipment, and many more. But what is Relay? How a Relay Works? What are the Applications of Relays? Let us explore more about relays in this guide. What is a Relay? A Relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a Relay is also a switch that connects or disconnects two circuits. But instead of a manual operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit. Relays can be of different types like electromechanical, solid state. Electromechanical relays are frequently used. Let us see the internal parts of this relay before knowing about it working. Although many different types of relay were present, their working is same. Every electromechanical relay consists of an consists of an Electroma

Chlorine dioxide Analyzer Principle

Chlorine dioxide measurement Chlorine dioxide (ClO2) is an instable, non-storable, toxic gas with a characteristic scent. The molecule consists of one chlorine atom and two oxygen atoms – represented in the chemical formula ClO2. It is very reactive. To avoid the risk of spontaneous explosions of gaseous chlorine dioxide or concentrated solutions, it is generally handled in dilution with low concentrations. ClO2 is soluble in water, but tends to evaporate quickly. Typically it is prepared on site, for example from hydrochloric acid and sodium chlorite. The procedure provides solutions with approx. 2 g/l ClO2 that can be safely handled and stored for several days. Image Credits : krohne Sensor Parts : Reference electrode Applied chlorine dioxide specific potential Current needed to maintain the constant potential Counter electrode Measuring electrode The disinfection effect of ClO2 is due to the transfer of oxygen instead of chlorine, so that no chlorinated byproducts are formed. ClO2

TILI Automation

Search This Blog