20+ hours banging head off wall...circuit diagrams problems

[bowlingo]

Hi all,

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

Here is the transmitter

https://www.omega.co.uk/ppt/pptsc.asp?ref=CDTX300

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

**broken link removed**

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

**broken link removed**

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. I have gone as far as I can with there tech support and the only option now is a refund. I am sure it is a wiring issue.

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

https://www.omega.co.uk/ppt/pptsc.asp?ref=CCT

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

Thanks

 

[bowlingo]

**broken link removed**

This is a modified diagram someone from another forum did for me (notice the MA1 and MA2 connections) this however has not worked

 

[Reloadron]

This link you provided is a signal conditioner? You don't need a signal conditioner or two for that matter.

The CDTX-300 that you have is a pH and Conductivity transmitter with isolated 4-20 mA outputs for pH and Conductivity. It has two isolated analog outputs of 0 to 14 pH = 4 to 20 mA and 0 to 10 mS = 4 to 20 mA. It is powered by a 12 to 24 VDC power source. It is not loop powered and your drawing makes no sense. Simply connect the power supply to the transmitter. Get the power supply disconnected from the outputs of the transmitter. You have run a risk of damaging the transmitter with that drawing. Now the outputs should be 4-20 mA individually isolated. That is all there is to it.

If you want other than 4-20 mA out then you place a resistor across the outputs of for example 500 Ohms (Precision) will give you 0 to 10 volts or 250 Ohms (Precision) will give you 0 to 5 volts, this is if you want to drive an ADC or something.

<EDIT> My bad, this unit does use an external Power Supply for the outputs from what I read in the data sheet as you posted. The drawing on the left should work using a single supply observing polarity. Now if your meters do not have isolated inputs that will cause a problem. Meaning if the external current meters share their power and signal common there will be problems. Have you tried using a simple hand held DMM to measure the currents individually? </EDIT>

Ron

 

[bowlingo]

The problem is at the SMS controllers as they are sharing some kind of common - or + somewhere. I have found this by seperating all the input and output wiring from one and having one of the transmitters outputs connected to it. This will end up turning into a nightmare trying to find what they are sharing...

would a signal isolator work? like this one https://www.omega.co.uk/ppt/pptsc.asp?ref=CCT

Due to the sms controllers sharing something I am not sure if this will work

Thanks

 

[Reloadron]

When I found the manual for the unit CDTX-300 and read through Power Connection and Output connection and neither mentioned the need for externally powering the outputs. Then I read the Calibration section where they use standard buffer solutions and simply say place a DMM set for mA across the outputs "Connect a DMM to the output terminals and set it to read current". The same for pH and mS. No mention of needing to power the outputs. Finally when you get to Outputs do they show what you posted. How the hell can a calibration as in preceding section be performed if external output power is needed.

I agree you have a power problem. I would try setting things up exactly as the drawing (single supply) on the left. Leave out one current meter. See if only using one meter works, then try the other disconnecting the first you tried. Use an isolated meter like a hand held DMM, not any panel meters.

I still do not see where a signal conditioner as you link to will be of any help. What are the SMS controllers you refer to? You have the CDTX-300 pHY / mS transmitter, the power supply (as I mentioned configure for a single supply) and the current meters. Unless you are calling the SMS the power supply? If I have a SMPS I generally call it a SMPS rather than SMS but I guess that is fine if it is the power supply you reference.

Try the outputs one at a time as I suggest using a single supply as shown in the drawings.

Ron

 

[bowlingo]

Hi Ron,

The SMS controller im refering to is one of these..

http://gsmalarmsystem.en.alibaba.co...10821650/GSM_SMS_Auto_Controller_RTU5011.html

Here is the manual

**broken link removed**

I have 2 x sms controllers one is using its analogue input for PH and the other is using its analogue input for CF as above all is well when using either the PH or CF on there own but when i am trying to use both cf and ph the readings go all over the place....this is due to the 2 x controllers using a common point within the system I have built. I have tried a power supply on each controller, a power supply on the control side of the sms controller (relays etc its switching) and one on the ph/cf transmitter...nothing seems to work. If I were to put one of these http://www.omega.co.uk/ppt/pptsc.asp?ref=CCT on the sms controllers analogue input for ph and one on the sms controllers analgue input for cf would that not work? I am wiring it exactly as the first drawing.

Thanks

 

[Reloadron]

Now I finally get it. The problem is most likely the SMS device which I now understand. The SMS device has 4 analog inputs. The problem is they all share a common ground as I read. This would have gone much better if your SMS device allowed differential inputs rather than single ended sharing a common ground. OK, now using a signal conditioner with isolated outputs may make more sense. Seeing the data sheet it makes sense now. Let me think about this and I will get back to you tomorrow from work or if work is busy later in my day from home. Do you have the Omega unit set up for current out?

Also, if another member wishes to jump in please do.

Ron

 

[bowlingo]

I am running the PH side through 1 seperate sms controller and the cf side through another seperate controller and have them connected each individualy between AGD and AG0...I was almost jumping with joy earlier when I managed to manipulate the scale and base settings on the analogue input so it was measuring the CF spot on againsy my calibration solutions and hand help meter I was restarting the units etc and all was remaining spot on.

What happened then was I tried to do the same with the ph..I took the probe out of ph4 buffer solution and put it into ph7 buffer solution this then made the cf probe jump from 0 (probe as in free air) to 2.5..I then put the ph probe into ph10 buffer solution and the CF reading went up to around 7 still whilst in free air.

This tells me the cf and ph outputs are not actually seperate on the transmitter this is using the top diagram as of this post...if I can get them to seperate i.e hopefully correct the wiring I am pretty sure I will be able to manipulate the base and scale settings on the transmitters and get it to measure acurately.

Thanks

 

[bowlingo]

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

https://uk.rs-online.com/web/p/prod...552267573743D343636323231342677633D4E4F4E4526

https://www.electro-tech-online.com/custompdfs/2011/10/0900766b803b8ed4.pdf

Maybe I can get away with using one as they are very expensive

Does this make sense?

What I am trying to picture is if the sms controllers are using a common point i.e through the power supplies etc and due to the sensitivity if this will still cause a problem although they will have floating inputs?

Thanks

 

[Reloadron]

What you need is a device similar to this unit. The problem you face is really two fold. As I mentioned earlier and Omega confirmed today on the phone is that the SMS device has analog inputs that share the same common, called a single ended input. If the SMS device had differential inputs there would not be a problem but it doesn't. Next, the Omega pH and mS transmitter is a bit unusual because the + are tied to the power positive and not a common negative. All of this could really have been better planned out but that is after the fact since you have the parts already. What you really need is a dual isolation system where the inputs are isolated totally from each other. The item I linked to is an example. I would think Omega makes such units and am surprised they did not suggest one. Yes, isolators of this type are expensive, unfortunately I don't see an easy way around it based on what you already have. Again, the problem is really two fold.

Ron

 

[bowlingo]

What you need is a device similar to this unit. The problem you face is really two fold. As I mentioned earlier and Omega confirmed today on the phone is that the SMS device has analog inputs that share the same common, called a single ended input. If the SMS device had differential inputs there would not be a problem but it doesn't. Next, the Omega pH and mS transmitter is a bit unusual because the + are tied to the power positive and not a common negative. All of this could really have been better planned out but that is after the fact since you have the parts already. What you really need is a dual isolation system where the inputs are isolated totally from each other. The item I linked to is an example. I would think Omega makes such units and am surprised they did not suggest one. Yes, isolators of this type are expensive, unfortunately I don't see an easy way around it based on what you already have. Again, the problem is really two fold.

Ron

Thanks Ron...

the device youve given a link to will work the same as two of these ones?

https://uk.rs-online.com/web/p/prod...552267573743D343636323231342677633D4E4F4E4526

the only difference as I see it is the one youve suggested can be used for voltage also?...would the sms controllers need voltage on its analogue inputs to function?

I also notice youve called the sms devices "sms device" I have two of these one for PH (transmitters output 1) and one for CF (transmitters output 2) this is why its confusing the hell out of me as its 2 independant sms controllers but due to the complicated way the systems been wired I would have to rebuild it to find out what is sharing what etc i.e negative in the system shared between the sms controllers due to being interconnected with a relay etc. I have tried 2 x different power supplies (one on each sms controller) but have left all the rest of the wiring connected which is about 20 wires on each sms controller going off to various relays etc to switch things on and off.

 

[bowlingo]

Sorry in my last reply I didnt explain...

on sms controller one....one wire from the transmitters PH output is going into the common (single end) and the other wire from the transmitters PH output is going into terminal 1

on sms controller two...one wire from the tranmsitters CF output is going into the common (single end) and the other wire from the transmitters CF output is going into terminal 1

**broken link removed**

**broken link removed**

 

[Reloadron]

I assumed a single SMS device only because when I read the data sheet it mentioned it had 4 analog inputs so I assumed you were using 2 of the 4 available. I don't know if they share a power common on their input commons. Wow, you have yourself one hell of a project.

Reading the data sheet I think the isolators you linked to would work. I noticed they were loop powered but have isolated outputs.

Ron

 

[bowlingo]

Someone from another forum has posted the following...

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...



https://www.electro-tech-online.com/custompdfs/2011/10/0900766b803b8ed4-1.pdf



https://www.electro-tech-online.com/custompdfs/2011/10/0900766b80d575b0.pdf



the weidmuller is the MCZCCC



Thanks

 

[Reloadron]

You do not want this unit. Devices like this are loop powered. What that means is they get their operating power by running the current through the input through a resistance. The source current is driven by a voltage and in your case 24 VDC.

Ron

 

[bowlingo]

You do not want this unit. Devices like this are loop powered. What that means is they get their operating power by running the current through the input through a resistance. The source current is driven by a voltage and in your case 24 VDC.

Ron

Is this not loop powered also?

https://uk.rs-online.com/web/p/prod...552267573743D343636323231342677633D4E4F4E4526

 

[Reloadron]

Yeah, but will take the higher compliance voltage.

Ron

 

[bowlingo]

Thanks Ron...

I have them arriving tomorrow from RS...I am hoping the cheaper one will work and I will return the ones I dont need...Are you saying go for the more expensive one even if the cheaper one will work because it will be better and more accurate?