What is 4-20 ma?

This article will be geared towards the curious, I am not going to try to train you how to work with the subject materiel.
But you will be able to converse intelligently after reading this.

BASIC DEFINITION

4-20ma can be either an input or output from the perspective of a PLC, (Programmable Logic Controller)which was covered in an earlier article.
The PLC specialty cards necessary are referred to as Analog cards(both input and output types).

MA stands for milliamp, a measurement of current flow. 4-20 is the lower and upper limits of this defined scale.
One example is the use of this scale to order a motor to run at a specific speed, with 4ma representing stopped and 20ma representing full speed.

Continue reading “What is 4-20 ma?”

A little about PLC’s

It seems to me that most information available on this topic assumes a moderate knowledge level before beginning their discussion, so I intend to break this down a little to accommodate those of you who may not have even heard of PLC’s before today.  Along the way, I will share my perspective as someone who has been working “hands-on” since the late eighties.
The most basic form of PLC’s are hardened, industrialized PC’s which provide inputs and outputs. Continue reading “A little about PLC’s”