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0-10VDC and 4-20mA. The Most Popular Analog Signals. Why Use One Over the Other. Voltage Drop?



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hi this is Tim and today we're going to

talk about the two most popular type of

analog signals used in industrial

applications and that is the milliamp

signal and the DC voltage signal the

start of the balton signal your typical

analog voltage signal is going to be 0

to 10 volt you see a lot of this and

drive applications where you're

controlling a drop speed you'll see it

be 0 to 10 volt also if you have an

application that needs to get reversed

they'll typically see this signal simply

reverse making it a minus 10 to +10

analog signal and this is used a lot in

servo applications the other type of

signal it is the milliamp signal which

is a little bit tougher to comprehend

initially but it's a much more robust

setup for field instrumentation which

makes it much more popular but before we

talk about the milliamp signal let's

talk about the problem with our DC

voltage analog signal and that's voltage

strong every foot of wire you have has

resistance and every corroded terminal

also creates resistance and each amount

of resistance you've added in a loop

creates voltage drop so let's just jump

right into a voltage drop calculator so

here we're gonna select 22 gauge wire

which is a very common signal size and

our voltage is gonna be 10 volt DC and

let's say we have 1 amp of lay now a

signal load is not gonna pull 1 amp but

I want to make the air much more obvious

to you if her cable is 1 foot long then

the voltage on the other end our cable

is going to be nine point nine six eight

bolts and chances are that's okay for

our application if it's ten feet long

it's gonna be nine point six eight volts

or 0.3 volts less than before now let's

make it a hundred foot long which isn't

that unusual for a field instrument the

voltage on the other end is gonna be six

point seven seven volts now when I put

out something like this someone always

comments and says well you should hook

the shield up to prevent this from

happening

Chioda cable is for reducing No

in Ain a lock circuits it does not deal

with voltage strong okay I'm not gonna

get into details of how voltage drop

works because there's a lot of great

articles out there on that so just

Google pollsters drop know what I what I

do want to do is give one practical

application showing voltage drops of

facts on an industrial application so I

have a regular voltmeter set the DC

bolts here I have our analog simulator

and I have a thousand-foot of 24 gauge

wire and what I want to do is show you

the difference in the signal with a

three foot connection to our meter up

here in a thousand foot connection to

our meter so here I have our analog

simulator hook to this meter with a

three-foot piece of wire just a verify

look at this fold meter right beside the

simulator and you see they in a lot of

simulators putting out Tim bolt and our

display is showing 10 volt now I'm gonna

do is I'm gonna add this thousand foot

work a wire into the circuit so I'm

going to take the positive terminal all

of our analog simulator and I have this

wire here connected to this full of wire

and then this fire here is the other end

of it so I'm a slot event our host you

see it says 10 ball here but we're only

showing nine point eight bulb over here

now just to verify that nothing is going

wrong with our simulator we're going to

connect ammeter our simulator is putting

out 10 volt but by the time we go

through all of this water here it's

creating enough resistance and voltage

drop they were only getting not going to

able to our meter and that's the problem

with the voltage signal is that over any

amount of distance you're going to have

voltage drop now in a control cabinet

where components are really close

together this is

lots of an issue and that's why you'll

see drive speed commands and various

internal components be voltage signals

but you almost never see a voltage

signal actually X to the control cabinet

for signals exiting the control cabinet

where the distance can be longer and the

environment can be more harsh we need a

different type of measurement and that's

going to be amps I like voltage where

resistance can create voltage drop if an

amps goes into a wire it must come out

the other side now one other thing to

think about on the voltage signal before

we disconnect all this is there is

another issue is if we take this down to

a command of zero so now we have zero

volt here and we have zero volt here how

do you know the difference between the

commander zero volt and a wire being

loose that's the other advantage of a

milliamp signal which we're going to get

into a little more in a second but it is

a 4 to 20 milliamp signal that means it

has what they call a lot 0 that way if a

wire is loose it'll show you 0 milliamp

when we know then that we have a

malfunction in the circuit now let's

just show how this is going to work with

this Millie I'm single

so if you'll give me just a second I'm

gonna modify our signal to accept a

milliamp instead of a voltage signal

alright I have this wiring família now

which will be this lower display and

we're gonna go to current to our mode

and we can bring this up I'm gonna take

it up to 20 milliamp you see it says 20

milliamp right here and also says 20

milliamp right here

now I'm gonna take this wire loose and

it will put the thousand foot roll of

wire in the circuit also one neat thing

about our analog simulator is as soon as

I take that well if you see it says open

wire on and now so now I will take that

hi it there and put the other end of the

spool through it and I'd like the

voltage signal where we saw a drop when

we put the thousand put a wire in line

you seen Alice

milliampere and it also says 20 mili-amp

over here and that's the advantage of a

milliamp signal with the exception of

you know leakage current and things that

will address in the troubleshooting

section of the series milliamps in

equals milliamps out so as long as your

load is not too high that it can't drive

the signal you'll have the same signal

at your instrument that you're going to

have at your PLC input

I hope this videos been helpful feel

free to ask any questions in the

comments and the next video we're going

to start wiring analog signals so we're

gonna why our potentiometer here both to

the meter that's facade of and also to a

PLC input and start understanding

exactly how to make these circuits work

till next time hi this is Tim and this

is amber of TW controls we run the

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