Analogue interface conundrum

atomic10

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Join Date
Jun 2013
Location
Australia
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11
Went to commission an industrial ventilation fan this afternoon that has a 0-10V speed control and found that the fan unit has and requires its own source for the 10V control, ready to be connected to a potentiometer. I am looking to connect it to either a micrologix analogue output module or Weidmuller TCP MODBus analogue controller which are both source units too.

Being a man of the digital age, this analogue interfacing has me scratching my head.

Can anyone recommend an isolation unit or digital potentiometer or a clearer mind than mind on how to interface this system?
 
Voltage is voltage. If your analog output card is 0-10V and the speed reference input to the drive is 0-10V then you can connect them. Just leave the 10V source terminal on the drive disconnected.

Just make sure it is actually 0-10V.
 
Cheers Saffa. My only trepidation was not knowing the internals, so wasn't sure if that was the normal thing to do. It was my first instinct, but thought there might be a 'industry standard' isolation method like interposing relays or optocouplers like we do for digital inputs.
 
"Voltage is voltage" as long as the reference (usually ground, but not always) is the same. Ground references at different potentials is called common mode.

If the grounds are at different potential then an isolator/repeater module would be needed.

Check for common mode: Put voltmeter on the DC volts range. Put one probe on 0V on one device, put the other probe on 0V on the 2nd device. If they're at the same potential, the DVM reads 0V. If the DVM reads anything other than 0V, then there's a common mode potential difference.
 
Went to commission an industrial ventilation fan this afternoon that has a 0-10V speed control and found that the fan unit has and requires its own source for the 10V control, ready to be connected to a potentiometer. I am looking to connect it to either a micrologix analogue output module or Weidmuller TCP MODBus analogue controller which are both source units too.

Being a man of the digital age, this analogue interfacing has me scratching my head.

Can anyone recommend an isolation unit or digital potentiometer or a clearer mind than mind on how to interface this system?

There is such a thing as a digital potentiomenter, but, I'd be more inclined to put a 0-10 to 0-10 isolator in, -tie the commons together- and call it a day. The +10V output on the drive is optional...it is the common that counts.
 
Voltage is voltage.

This is an incredibly dangerous comment to make. Voltage in some parts of the world is defined as "potential difference", meaning the different of electric potential between two points.

Voltage between two lines or between line and neutral will both be voltages, but only one will likely be right for your application. The same will apply to DC... assuming the ground or common is the same is a mistake.

@atomic10, when you say it requires it's own source, does the wiring diagram show the fan unit supplying the voltage to the potmeter, or does it show an external power supply supplying the potmeter and the fan takes in the center tap and common off the potmeter?
 
Cardosocea brings up a good point. You can't really answer this without seeing the wiring diagram or at least you shouldn't try. My many years in this industry has taught me that different equipment manufactures will use different terminology to mean the same thing or the same terminology to mean different things but a wiring diagram (done correctly) is a wiring diagram and will tell you how you can and should wire the unit up. A floating ground on both ends could cause anything from poor accuracy to damage so you really need to know how the manufacture shows it being wired.
 
This is an incredibly dangerous comment to make. Voltage in some parts of the world is defined as "potential difference", meaning the different of electric potential between two points

So you believe that 5 Volts DC in the UK could be different to 5 Volts DC here in NZ? Voltage and potential difference are different names for exactly the same thing: joules per coulomb charge.

Of course one needs an understanding of the reference point (0V, GND, VEE, V-, VSS or whatever you want to call it), but if your reference points are tied together, i.e. at the same potential, then the voltage produced by the output device will be correctly interpreted by the input device.

Of course that isn't always possible depending on circuit design internal to each device, but I have come across very few devices in my career where I wasn't able to connect the commons and have everything work nicely, and I have never damaged a device by doing so. Maybe just lucky?

In the handful of cases where things didn't work (almost always 4-20mA loop devices), adding an isolator as jdbrandt suggested has resolved the issue.
 
So you believe that 5 Volts DC in the UK could be different to 5 Volts DC here in NZ? Voltage and potential difference are different names for exactly the same thing: joules per coulomb charge.

No... it's the definition of voltage that can and does catch people out, which by OP's starting post was clear that he was confused with.

I can also say that current is current, and it means exactly the same, i.e. nothing.

Edit: Sorry for the tone. But I am in the UK and am tired of people using the "<something> means <something>" sentence to dodge explanations and clarifications.
 
Edit: Sorry for the tone. But I am in the UK and am tired of people using the "<something> means <something>" sentence to dodge explanations and clarifications.

All good, I should maybe have worded things better. One of the negative consequences of typing on a mobile is a tendancy to be brief, which isn't always beneficial on a forum.

By now I'm sure the OP has given up on getting anything more from us, followed conventional Aussie wisdom of "she'll be right" and just given it a crack. Hopefully he reports back with any lessons learnt.
 
No... it's the definition of voltage that can and does catch people out, which by OP's starting post was clear that he was confused with.

I can also say that current is current, and it means exactly the same, i.e. nothing.

Edit: Sorry for the tone. But I am in the UK and am tired of people using the "<something> means <something>" sentence to dodge explanations and clarifications.

Totally Off Topic...but "Brexit means Brexit" springs to mind, as an example of government-dodgy-speak...:mad:
 
By now I'm sure the OP has given up on getting anything more from us, followed conventional Aussie wisdom of "she'll be right" and just given it a crack. Hopefully he reports back with any lessons learnt.

Appreciate all the replies and healthy debate gents. Hooked it up with the war cry of " 'ave a go mate" and it works a treat. (y)

For those interested I am using a Weidmuller UR-20 TCP Modbus Analogue I/O module controlled by a Micrologix 1400. The Fan is a PowerLine Ultra EC Series from Fantech.
 
atomic10,

you need to look at the wiring diagram and post a picture for us and give us a manufacturer and model number of the unit.
from your description, your drive has its own power source (10V) and you need to connect a pot to it to determine the drive speed.
so, from that description, you have dc+, DC common, and very possibly a 3rd wire for the pot input to the drive.

the reference to this was a dangerous comment comes from the way the drive is wired and how you plan on wiring the output to the drive.

I am not certain that you can do what you suggest.

james

my post was very late in sending, Glad it worked.
 

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