Continued from the previous post
In practice, all these process controllers incorporate a microcontroller.
But microcontrollers are programmed in assembly or in C language, so to create a function block programmable process controller from a C programmable microcontroller, an intermediate firmware must be written.
Continue reading Internal workings of process controllers II.
This time the internal workings of a process controller will be shown.
I’ll show it through a Siemens SIPART DR24 process controller.
Its user manual can be found on the Siemens’ website:
Siemens SIPART DR24 manual
Although it is almost obsolete, the operational principles can easily be demonstrated with it.
Continue reading Internal workings of process controllers I.
This is just a brief overview of how to do thermocouple measurements correctly and simply.
The principles of measuring with thermocouples are described by a lot of web pages. However, one can easily misinterpret the informations obtained form the internet.
The first confusion usually comes from the use of “ice bath” as cold junction compensation, the other is when someone tries to use the thermocouples’ mV – temperature tables.
Continue reading Thermocouple Measurement Clarification
When a switch or a pushbutton has to be connected to a digital circuit it is often (almost always) a nasty thing, because its unwanted behaviour.
It is a common practice to connect a button or a switch to a digital system (to a microcontroller, to a PLC, or to a PC). The simplest way to do it is shown in the picture below:
Connecting a pushbutton to a microcontroller
If we measure the voltage at the input of the microcontroller with an oscilloscope, it would show the following:
Contact bouncing phenomena
The problem is obvious. There isn’t a simple, clean low to high transition. If the microcontroller is fast enough, it senses this switch on event as if there were several pushbutton pressings.
Continue reading Switch debouncing in PLC software