Practical Tips and Techniques
DC Solenoids are the worse culprits for electrical surges in your system. When the electrically generated field collapses, an opposite polarity voltage is generated. This voltage spike can be high enough to weld the contacts on a PLC output relay. To protect your PLC output relay, use a diode to ensure that the voltage spike … Read more
In part 1, we looked at writing PLC programs to control a traffic light using discrete bits and timed sequencing using indirect addressing. We will now look at how we can use indirect addressing for inputs and output to control the sequence in the program. Let’s look at an example of controlling pneumatic (air) cylinders. … Read more
What is the best way to program a PLC? My answer is simple. The best way is one in which someone can look at your program and understand it. I cannot stress the need for good documentation of your program enough. The best programs are ones that I can return to after several years and … Read more
Programmable Logic Controllers (PLC) will scan very quickly. This can be anywhere from 1 to 20 ms, translating into 1000 to 500 times each second. But what exactly is a scan? A scan is when the PLC will complete the following: Read Inputs: Look at all of the inputs to the programmable controller. Digital, Analog, … Read more
Most programmable controllers will come with an RS232 communication port. This recommended standard (RS) has voltage signals between 3 to 15 volts DC concerning the ground/common pin. RS232 devices are called DTE (data terminal equipment) or DCE (data communication equipment). The maximum cable length for the communication cable is 15m; however, depending on the environment, … Read more
In industrial environments, we often get noise on the analog signal input to PLCs or other controllers. Motors, lousy wiring, etc., can generate noise. Placing a 1- 100 uF capacitor on the input signal and ground (common to the cabinet) will reduce the noise the input receives. If you have any questions or need further … Read more
