Interposing relays

omsumitam

Member
Join Date
Jul 2009
Location
New Delhi,India
Posts
23
What is the use of Interposing relay,

Is it only required for solenoid Valves because of different requirement Voltage (PLC is restricted to 0.5A at 220 VAC, but the solenoid which is to be connected to the relay requires 1.2A at 220 VAC.)

Can/Why we use it for Analog Signals .
How it works in the whole operation , in brief ? .I know its very basic. If any one can help me out of this .

Thanks in advance !!
:rolleyes:
 
Relays can handle:
1) Voltage differences
2) Isolation
3) Switching analog signals (How does a PLC switch analog signals?)
4) Driving more current
5) Acting as inexpensive sacrificial elements.
6) Switch multiple loads at one time.
7) (optionally) Being a manual override.
8) Accommodate larger wire's then typical PLC modules.

You're right. Basic question.
 
You're forgetting relay logic. Although these days I only ever use relay logic to punish my apprentices and for my own sick amusement...
 
Thanks .



so can a general system be described in the following way leaving apart are the Data highway, redundancy, etc.

i am here concerned about the Blue lines i.e., after Relays
 
I have no idea what your are "Concerned" about. A relay is an electromechanical switch. That's all.

@Jeev - Thanks, you know, it's been so long myself I didn't think of that, but it's a valid use. Logic circuitry.
 
Mr. rdrast
Your Answer is right but problem is with your attitude.
What you r telling , can be easily searched on google, so keep that information with you. we r here to share and solve the probs of self and other and increase the knowledge ,
if u r not concerned about that .
SHUT UP.
 
@Jeev - Thanks, you know, it's been so long myself I didn't think of that, but it's a valid use. Logic circuitry.

Just recently I saw a simple machine out in the field that was controlled entirely by 2 VFD's, some sensors with delay timers built into them and a handful of relays. Needless to say the hobbyist and tinkerer in me was highly amused.... The Engineer in me was appalled, hahaha.


omsumitam - You're still going to need something to drive your Analogue Field Devices properly.
 
Mr. rdrast
Your Answer is right but problem is with your attitude.
What you r telling , can be easily searched on google, so keep that information with you. we r here to share and solve the probs of self and other and increase the knowledge ,
if u r not concerned about that .
SHUT UP.

Ask a real question then. I'm not going to give you an introduction to electronics and controls. See ya... Ignore on.
 
Mr. rdrast
Your Answer is right but problem is with your attitude.
What you r telling , can be easily searched on google, so keep that information with you. we r here to share and solve the probs of self and other and increase the knowledge ,
if u r not concerned about that .
SHUT UP.

No need to be rude. To address your concern about the blue lines:

1) The Relay's will switch your signals on and off.
2) You will need an Analogue Output Module on your PLC to control your field devices (And motors if they require Analogue control) through the switching relays.
3) You will need a Digital Output Module on your PLC to switch your relays.
4) Your relays might isolate your Digital control, but they will not isolate your Analogue control between the 2 systems, so make sure your earthing, Shielding and COMM/Analogue Refernce is wired correctly.

Ask a real question then. I'm not going to give you an introduction to electronics and controls. See ya... Ignore on.

Don't let the pixels make you angry.
 
Sumit: rdrast's answer was right on the money. Google on relay usage, and take your pick of applications. Better yet, ask your teacher. In short, relays can be used to amplify the DO's capacity, isolate it from the field wiring, and so on.

Only time I've seen them used for analog signals was when they wanted to add some readings without spending on an extra analog card, the rack was full anyway. Having DOs available we scrounged up a handful of relays and cooked up a kind of slowpoke multiplexing sample and hold using one AI.

Oh, google on the meaning of 'interpose', in case that's your doubt.
 
Last edited:
Only time I've seen them used for analog signals was when they wanted to add some readings without spending on an extra analog card, the rack was full anyway. Having DOs available we scrounged up a handful of relays and cooked up a kind of slowpoke multiplexing sample and hold using one AI.


It's actually not that uncommon... I've seen many cases where low sample rates were acceptable and this method was used to keep the system simple and cost effective. Not to mention many Microcontrollers will internally multiplex ADC channels to increase the number available to the user without incurring all the overheads of the individual channels. I'd almost put money on it that some Analogue Input cards do this too...
 
rdrast posts = 2753
omsumitam posts = 22

I think omsumitam needs to find somwhere else to play while the real men around here get some work done.

P.S. rdrast, I always enjoy reading your input. Thanks for sharing your knowledge.
 
Mr. rdrast
Your Answer is right but problem is with your attitude.
What you r telling , can be easily searched on google, so keep that information with you. we r here to share and solve the probs of self and other and increase the knowledge ,
if u r not concerned about that .
SHUT UP.

:rolleyes:

Dude, you are the only one here i can see with the wrong attitude !
 

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