Problems analogue signal
Problems analogue signal
(OP)
Hi,
I have the following problem. I am suppose to receive a 4-20 mA signal from a system called TELEFLO DIVA supplied by Air Liquide.
Problem arises that when i connect the two wires to our plc input card (configured as active) we read nothing. However wheni connect a 4-20 mA generator (as passive) and generate to the card it read ok. I belive the signal is given in parallel and not in series, could this be?
I attach the diagram that was given to me.
I have the following problem. I am suppose to receive a 4-20 mA signal from a system called TELEFLO DIVA supplied by Air Liquide.
Problem arises that when i connect the two wires to our plc input card (configured as active) we read nothing. However wheni connect a 4-20 mA generator (as passive) and generate to the card it read ok. I belive the signal is given in parallel and not in series, could this be?
I attach the diagram that was given to me.





RE: Problems analogue signal
From your text description, it sounds like the Teleflo Diva is a four-wire device and the PLC is expecting a signal from a two wire device. That can be corrected with a signal isolator.
xnuke
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RE: Problems analogue signal
I think the second picture tries to say its 4 wire, however when we generate mA with a Fluke to their terminals it seems to work, so i dont kno what difference ther can be between the Fluke and this Teleflo DIVA of which a find no info on the web btw.
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
Correct me if I am wrong but this is how I understand this.
If I want the 24 Vdc supply to come from the TELEFLO I configure my card as Passive and connect to terminals 14 and 12 on the Teleflo, On the contrary if I want the 24 Vdc supply to come from my card I configure my card as Active and connect to terminals 13 and 12 on the Teleflo.
RE: Problems analogue signal
Try the configuration on the attached drawing. Set the jumper on the analog card from FP to COM (I think Passive is how you refer to this setting). If the loop still does not work, please let me know.
RE: Problems analogue signal
thanks for your help
RE: Problems analogue signal
Please try the new configuration in the attached drawing.
RE: Problems analogue signal
RE: Problems analogue signal
I noticed I posted the ACAD drawing file (.dwg) instead of the .pdf file. Please find the .pdf file attached below.
I chose the new wiring configuration based on the observation the Teleflora analog ouput is a "sinking" output. However, even if the new configuration works, I would not be comfortable with this wiring arrangement. The Metso analog input card is a single-ended card. On a single-ended input card, all channels share a common connection. The wiring diagram I posted basically sets the analog output from the Teleflora on "top" of the channel's 249 ohm resistor. I do not know what kind of interaction this configuration would have with other channels on the input card.
Do you have a circuit diagram for the Teleflora analog output (similar to the diagram for the analog input found in the instruction manual you posted)? This information would be helpful.
Finally, the easiest way to get the loop working, as xnuke suggested, is to utilize a signal isolator.
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
I would really like to find a solution to your problem. Is there any way to obtain a circuit diagram for the Teleflora analog output?
RE: Problems analogue signal
Ok. If you get the loop working, please post the solution.
Also, sorry for the misspelling of Teleflo.
RE: Problems analogue signal
RE: Problems analogue signal
If you can connect the Teleflow to the analog inoput card and take some voltage measurements at various points. For example measure the voltage across the output of the Teleflow, then again across the analog input card. The dirty secret here is that the analog input card is really measuring voltage, not current. A 250 ohm resistor is placed across the voltage inputs so that a 20 ma signal will produce 5 volts to the ADC.
RE: Problems analogue signal
You said your PLC works OK when you simulate a Passive signal (thats a 2 wire input meaning the Fluke is just creating a load on the input, not suppling the power). In other words you are trying to supply the loop power from both places.
If you re-configure your PLC input as passive it should work
Sometimes though you get into a situation where the inputs are not compatible because either both are referenced at different levels.
If it doesn't work please do a couple of tests and report back
With the plc input configured as passive see if the input terminals are grounded (measure input terminal to ground with multimeter.
Measure voltage at each of the flowmeters terminals to ground.
Connect up the flowmeter to the input module and once again measure the voltage between each plc input terminal and ground.
Disconnect the positive wire at PLC terminal and connect a mA meter in series, do you get mA?
Disconnect the negative wire at the PLC what is the current in positive wire now?
BTW, by ground, I am refering to the chassis, not negative what are you calling Ground in first sentence of my reply?
RE: Problems analogue signal
Active output TELEFLO and passive PLC Input. FAILED
Passive output TELEFLO and Active PLC Input. FAILED
Passive output TELEFLO and Passive PLC Input. FAILED
Active output TELEFLO and Active PLC Input. Have not tried.
GND in TELEFLO is connected to earth
Negative terminal in PLC input also connected to same earth.
When I set the input card as Passive I set up the multimeter as Active, generate a signal and it is received.
When I set the input card as Active I set up the multimeter as Passive , generate a signal and it is received.
The input card works fine, we have many other instruments connected and never had a problem. I believe the problem is the way the TELEFLO generates the mA.
One thing I haven't mentioned is that when I set-up both sides as passive and connect the negative of the plc card to another negative of another card I do read mA but the the actual mA I should be reading, it reads a fixed value of mA.
This is becoming a headache, We have commisioned this solar plant with around 1500 signals and this one we cant get!!
I need to try the last two posts, reading voltages at different points.
Thanks
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
I vote YES
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Problems analogue signal
RE: Problems analogue signal
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Problems analogue signal
RE: Problems analogue signal
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Problems analogue signal
RE: Problems analogue signal
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Problems analogue signal
RE: Problems analogue signal
RE: Problems analogue signal
Contractors love those panel outlets for running their drills etc. I suggest you install a circuit breaker sized to protect the transformer.
RE: Problems analogue signal
I have tried using a level transmitter connected in parallel with the process and works fine. So I have ordered on to install and that way I will always have the level indication even if the TELEFLO goes down. Thanks everyone for their inputs.
RE: Problems analogue signal
Are you saying you got the Teleflow output working? If so, what did you do to get the output working?
RE: Problems analogue signal
It's quite common to find that especially in odd-ball transmitters, they don't bother to isolate the output from ground.
You could try this little test:
Put a 250 Ohm load on the Teleflo (active) and measure the voltage from ground to each terminal with the Teleflo at zero percent.
Make the same voltage measurement with your PLC as passive with your calibrator at zero percent, I think you will find the voltages to ground are different.
Please report back.
If you already have it working, let us know what you did.
Regards
Roy
RE: Problems analogue signal
Your PLC input is referenced to ground
So assuming the Teleflo Power supply is grounded you will get 24/250 = 96 mA as soon as you connect Teleflo + to PLC +
Unless you can isolate the Teleflo power supply from ground a signal isolator is the only way forward