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Old June 24th, 2010, 03:22 AM   #1
omsumitam
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Interposing relays

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 !!
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Old June 24th, 2010, 05:14 AM   #2
rdrast
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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.
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Old June 24th, 2010, 05:36 AM   #3
Jeev
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You're forgetting relay logic. Although these days I only ever use relay logic to punish my apprentices and for my own sick amusement...
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Old June 24th, 2010, 05:44 AM   #4
omsumitam
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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
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File Type: xls INTERPOSING RELAY.xls (19.5 KB, 57 views)
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Old June 24th, 2010, 06:13 AM   #5
rdrast
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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.
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Old June 24th, 2010, 06:22 AM   #6
omsumitam
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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.
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Old June 24th, 2010, 06:28 AM   #7
Jeev
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Quote:
Originally Posted by rdrast View Post
@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.
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Old June 24th, 2010, 07:30 AM   #8
rdrast
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Quote:
Originally Posted by omsumitam View Post
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.
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Old June 24th, 2010, 10:07 AM   #9
harryting
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I only see one dude with the crappy attitude and it ain't rdrast.
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Old June 24th, 2010, 10:21 AM   #10
Jeev
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Quote:
Originally Posted by omsumitam View Post
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.

Quote:
Originally Posted by rdrast View Post
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.
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Old June 24th, 2010, 10:25 AM   #11
ydtech
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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 by ydtech; June 24th, 2010 at 10:36 AM.
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Old June 24th, 2010, 10:36 AM   #12
Jeev
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Quote:
Originally Posted by ydtech View Post
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...
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Old June 24th, 2010, 11:36 AM   #13
TheStarr
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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.
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Old June 24th, 2010, 12:45 PM   #14
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I concur RSDrast answer is right on the money and it was informative without insult
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Old June 25th, 2010, 06:49 AM   #15
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Quote:
Originally Posted by omsumitam View Post
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.


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