Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Great post.
If it is so simple, how about you post up a simple schematic showing how a PLC can provide 24V, at the same time I cannot measure 24V anywhere (only the 0.9V, 3.6mA across the signal and return line). I get that a current source regulates voltage, but that doesn't explain how if an...
Well... if the instrument requires a minumum of 12V. There has to be a voltage drop of 12V on the instrument?
And let's say there was an external power supply, and you connect the 24V supply between CH1 (signal line), and the transmitter to supply the power, then there is 24V there.
... Hence...
Thanks. I checked a few voltage measurements today, and have a bit better understanding. For the analog input, the PLC has a return/common, and signal. Something like my attached drawing.
Where would the 24V be in this case if I am measuring the 0.9V drop across return and signal? 0.9V is the...
Thanks. What every one is saying makes sense; but try and clarify/focus on this point;
I measure 24V across the terminals of a PLC analog output. Line resistance drops 1V, and my Trip Amplifier uses a 5ohm impedance; so at 20mA it drops 0.1V. Where is the other 22.9V dropped? Why can't I find...
You have described the Analog Input circuit; a transmitter to the PLC. Let's say the wires drop 1V total, and the PLC has a 250ohm shunt. At 20mA then, we have dropped 5V at the PLC, and 1V on the line. The PLC provides 24V loop power. HOW does the transmitter dissipate this extra voltage?
And...
Errmm. Nothing crazy, just a transmitter to PLC for the analog input example, and a PLC to resistive shunt for a Trip Amplifier.
An example circuit for the AI is here; https://www.allaboutcircuits.com/vol_1/chpt_9/3.html
This is a generic theory question, not anything in particular to a...
Hi,
I was pondering the workings of 4-20mA loops for both inputs (transmitters to a PLC), and outputs (PLC driving an I/P or even a Trip Amplifier).
A loop powered instrument say has a PLC driving a 24V supply to the instrument. Lets say there is 1V drop on the cabling, and the instrument...
Well, I have been banging around the Internet learning (well I thought I was), about diodes, and protection and so forth; and I am pretty sure I have just confused myself.
Could someone check out this schematic I drew, check some of the comments, and tell me if I am about to blow something up...
How did you go with this?
I have had very similar problems - with symptoms ranging from MCU resets and garbled LCD displays.
The biggest help was when I put a 10uF cap across the regulator output that supplied the 5V to the MCU.
I still have an issue where, if the relay is active, and I...
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
