# Wiring diagrams...driving me insane



## bowlingo (Oct 9, 2011)

Hi all,

I am trying to get a PH-CF transmitter to work with SMS controllers analogue inputs..

Here is the transmitter

pH and Conductivity Transmitter

As you can see the transmitter takes the value of the PH and CF and then outputs them at between 4 - 20mA I can calibrate the system without problem using a multimeter i.e 5mS (half of CF range) = 12mA (half way between 4 and 20 mA)

They work great on there own i.e the PH side into the sms controller that is going to read the PH values or the CF side of the transmitter into the sms controller that is going to read Cf values....Until I have both on at once..when this happens the readings go crazy that the controllers read of which is due to them sharing the supplies in some fashion.

Here is the diagram provided by the company who sold me the transmitter









I have wired it exact and always the readings go crazy at the sms controller (but perfectly fine when wiring one or the other)

Here is the circuit diagrams provided with the transmitter










I have wired it in both combinations and used 3 x individual power supplies but no luck. You will notice the negatives are joined internally...I have opened the unit to confirm this. This means theres no way of seperating the supply apart from cutting the tracks inside the unit or similar. Due to the nature and affordability of this unit I am stuck with this one as I cant find anymore specific to my application that are not 3+ times the price.

On the website I bought the transmitter from you will see this...

Economical DIN Rail Signal Conditioners

This is a loop isolator..if all else fails with the wiring could this or something similar work?

Thanks


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## octaneman (May 13, 2009)

Hi bowlingo 


Judging from the diagrams it should work the way you have it set up, but I'm wondering if the transmitter program will _allow_ you to do both functions at the same time. The company's description of the transmitter says that the external power supply is _only_ if A/C is not available and should be set up according to the first diagram. Since both the Ph side and the Cf side work when its set up independently to get the readings, IMHO I don't believe its a hardware problem because if it were you would be getting gibberish on either the Ph or Cf side or no readings at all. 

Question: Are you applying any other analogue signal (aside from the a/c power supply) feeding through the controller ? 

Question: Are the probes in good condition or sensitive enough to get both readings ?


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## bowlingo (Oct 9, 2011)

Hi...
I have been on the phone to Omega technical today and someone else and they are saying the input on the 2 x sms controllers are not isolated inputs of which is causing the 2 x seperate sms controllers to interfere with themselves possibly through the negatives. They have told me to try a loop isolator on each input of which will make floating inputs as I understand it.
I have found these 
Buy Signal Conditioning Loop powered isol signalconverter,4-20mA RS MIN310 online from RS for next day delivery.
http://docs-europe.electrocomponents.com/webdocs/03b8/0900766b803b8ed4.pdf
Maybe I can get away with using one as they are very expensive
Does this make sense?
Thanks


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## octaneman (May 13, 2009)

bowlingo said:


> Hi...
> I have been on the phone to Omega technical today and someone else and they are saying the input on the 2 x sms controllers are not isolated inputs of which is causing the 2 x separate sms controllers to interfere with themselves possibly through the negatives. They have told me to try a loop isolator on each input of which will make floating inputs as I understand it.
> I have found these
> Buy Signal Conditioning Loop powered isol signal converter,4-20mA RS MIN310 online from RS for next day delivery.
> ...




bowlingo,


Omega has admitted that their device's inputs are _not_ isolated which makes the setup impossible to get both readings at the same time. Isolating the inputs would get the results you want but the company's instruction is to get an external signal isolator. The problem then _is_ a hardware issue because their unit is designed to operate on one mode at a time. Your only solution is to get the external box, if you try modifying your unit by cutting traces you risk permanent damage because you don't have the schematic to make such modifications without knowing the unit's PCB tolerance parameters. Whats worse even if you do succeed in modifying the unit by eye, the unit's tolerances will change and the likelihood of your readings being way off the mark will make all your hard work meaningless.

I can understand your frustration, you feel cheated and that you somehow can make both modes work without buying the extra gear. It's difficult at times to accept any company's explanation, but the engineers who designed it made sure that what you want to do with their unit won't be possible without extensive mods.


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## bowlingo (Oct 9, 2011)

octaneman said:


> bowlingo,
> 
> 
> Omega has admitted that their device's inputs are _not_ isolated which makes the setup impossible to get both readings at the same time. Isolating the inputs would get the results you want but the company's instruction is to get an external signal isolator. The problem then _is_ a hardware issue because their unit is designed to operate on one mode at a time. Your only solution is to get the external box, if you try modifying your unit by cutting traces you risk permanent damage because you don't have the schematic to make such modifications without knowing the unit's PCB tolerance parameters. Whats worse even if you do succeed in modifying the unit by eye, the unit's tolerances will change and the likelihood of your readings being way off the mark will make all your hard work meaningless.
> ...


Ok...do you think it is worth me getting and trying the external loop isolators?


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## octaneman (May 13, 2009)

bowlingo said:


> Ok...do you think it is worth me getting and trying the external loop isolators?







You're the only person who can answer that question. It all depends on the type of work you do, how often you will use the isolating unit to justify its cost for it to pay itself off in the long term.


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## bowlingo (Oct 9, 2011)

ok...Ive spent around £3000 on this system so its more a case will it work using loop isolators regardless of cost..bearing in mind the 2 x sms controllers are possibly sharing something i.e a negative within the complex input and output relays etc


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## octaneman (May 13, 2009)

According to the company's description of the transmitter: 

Q: A loop powered isolator may be required when connecting to data acquisition equipment. /:Q


That pretty much says it all but if you still have doubts, contact the company again and ask their technical department * specifically * what loop isolators would be recommended for * their* CDTX-300 unit. The company reps will jump on the opportunity to sell you one of their own models.


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## Stu_computer (Jul 7, 2005)

keep in mind you have a responsibility to the customer to supply a serviceable and parts replacable product...so no hacking the instruments. :grin:

the Weidmuller MCZ CCC Passive Isolator does the same thing and is cheaper (£77) and since the input side is conditioned it is likely that one isolator will do the job...and if not you still save about £60 compared to buying two RS MIN310.

Buy Signal Conditioning SIGNAL CONDITIONER,MCZ CCC Weidmuller 8648600000 online from RS for next day delivery.


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## bowlingo (Oct 9, 2011)

Just looked at the Weidmuller one its a lot cheaper than these ones that have just arrived today

Buy Signal Conditioning SIGNAL CONDITIONER,MCZ CCC Weidmuller 8648600000 online from RS for next day delivery.

I will test it later using one or two (hopefully one) if it works I will send the more expensive ones back and go for these cheaper ones.

Do they look exactly the same?

Thanks


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## Stu_computer (Jul 7, 2005)

both types clip onto the standard 35.5 mm din rail.

the weimuller is thinner...and looks more like a weidmuller wire terminal block, whereas the RS looks like a module.
Terminal Blocks | www.weidmuller.com


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## bowlingo (Oct 9, 2011)

Stu_computer said:


> both types clip onto the standard 35.5 mm din rail.
> 
> the weimuller is thinner...and looks more like a weidmuller wire terminal block, whereas the RS looks like a module.
> Terminal Blocks | www.weidmuller.com


I have just noticed the weimuller has an input range of max 15 volts..I am using a 24V power supply to power the transmitter.

please can you look at the 2 and tell me if theres going to be an issue with a 24V supply...

http://docs-europe.electrocomponents.com/webdocs/03b8/0900766b803b8ed4.pdf

http://docs-europe.electrocomponents.com/webdocs/0d57/0900766b80d575b0.pdf

the weidmuller is the MCZCCC

Thanks


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## Stu_computer (Jul 7, 2005)

the 24volt power supply is not a problem.

the input side is an clamping circuit (an 18volt zener diode. and the 20mA source signal has a 3volt drop) so the maximum voltage seen on the source side isolating circuit would be about 15volts.

part of the transmitter's function is managing the remaining voltage in a loop.

since the output side gets its power from the input side that will be about 10volts available to the load, which should be sufficient to power the load (instrument).

the isolator should be mounted close to the meter to minimize voltage drop in the wiring.

the wiring between transmitter and isolator will have some voltage drop but as long as its a large enough guage size and not an excessive distance then it should not be a problem.

the attached pdf file may be helpfull...


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