In our last newsletter we had a look at the Alpha Controller and some of the functions. This time, let’s have a look at a possible application of the unit.
You need to monitor the runtime of a motor which is supposed to run for a maximum of x seconds (x = time you want the motor not to exceed) Should the motor exceed this time, you want to force it to stop and lock it out to prevent a restart without physically resetting it. At the same time, you want to be notified of the fault.
Let’s start with the inputs you will need.
1 “run” signal. This could be a normally open contact on the motor contactor
2 “reset” button. This is the physical reset button that must release the fault lock-out
Now we will look at the output side. This is a rather easy one as we will be using one output only. This is the relay that will need to lock out the motor in the event of it exceeding the run time. We will simply connect the motor control circuit via this relay. That means when our output is on, the motor is stopped. This is one area where we need to pause and consider the application. We assume that this is not a critical application and that no damage would arise should the lock-out fail. If this is a critical application, we must ensure that we wire our circuit to “fail to safe” in the event of a power loss. Simply put, if we do not want to energise the relay for the fault condition but de-energise it. We will discuss that more in future
Back to our circuit. When we receive the input to tell us the motor is running, our timer will start counting. This timer is set to the maximum time we want the motor to run. If we exceed the time, we turn on a set coil, activate the display screen as well as a second timer. We will discuss the function of each separately.
Set Coil. This coil will turn on and remain energised even when the input to it is removed. The only way to de-energise this is to provide an input to the Reset which is provided by our reset button
Display Screen. When the screen is activated, it will display the message you set up. In this case we right click on the block, select open parameter dialog and click on the string radio dial. In the text box we will enter the required message. Lower down you will see the text x and y co-ordinates. Use these to set the start point of the text. You will also note that you need to set the length of the text.
Delay Timer. This timer is put in just to allow the screen to display the correct text before the GSM modem sends a sms for the alarm. Without this slight delay, you could get a message that only shows input/output status and no text.
Have a look at the screenshot below and write the program. Select the simulation mode and have a look at how it works, then improve it. Please note that this program was only set up as a tutorial. If you want to use it, please test it and ensure you take into account all safety precautions
Till next time, stay safe and remain passionate about your work. By the way, for those who have not had time to get their copy of the Manual for Electricians Volume 1, check it out on www.lulu.com/spotlight/SparkyHelp