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FP-AO-200 two voltage sources
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Little Dave
Nov 20, 2006, 3:10:15 PM11/20/06
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Hi all. I'm sure there's an easy answer to this question but I can seem to find it...
I have a Fieldpoint system and I'm using a FP-AO-200 module to send signals out to various devices. One of these devices is a Sierra MFC. The MFC manual includes the following passage:
"This instrument is not a loop-powered device! Do NOT apply power to the 4-20 mA output or input connections."
Unless I missed something, there is no way to isolate a given channel from the FP-AO-200 module loop supply.
My question is this: How do I connect these two pieces of equipment without damaging either of them? The closest answer I was able to find in the knowledgebase can be found here:
<a href="http://digital.ni.com/public.nsf/allkb/bf4b2f3568cb0d7086256b8e006ee07c" target="_blank">http://digital.ni.com/public.nsf/allkb/bf4b2f3568cb0d7086256b8e006ee07c</a>
There are a couple of key differences between that situation and my own:
1. I am using an analog signal, not a digital one.
2. I cannot disconnect the input device's power supply as suggested in the "To Connect a Sourcing Input to a Sourcing Output" section.
Can someone set me on the right path? Thanks in advance for any help.
Dave
I have a Fieldpoint system and I'm using a FP-AO-200 module to send signals out to various devices. One of these devices is a Sierra MFC. The MFC manual includes the following passage:
"This instrument is not a loop-powered device! Do NOT apply power to the 4-20 mA output or input connections."
Unless I missed something, there is no way to isolate a given channel from the FP-AO-200 module loop supply.
My question is this: How do I connect these two pieces of equipment without damaging either of them? The closest answer I was able to find in the knowledgebase can be found here:
<a href="http://digital.ni.com/public.nsf/allkb/bf4b2f3568cb0d7086256b8e006ee07c" target="_blank">http://digital.ni.com/public.nsf/allkb/bf4b2f3568cb0d7086256b8e006ee07c</a>
There are a couple of key differences between that situation and my own:
1. I am using an analog signal, not a digital one.
2. I cannot disconnect the input device's power supply as suggested in the "To Connect a Sourcing Input to a Sourcing Output" section.
Can someone set me on the right path? Thanks in advance for any help.
Dave
centerbolt
Nov 20, 2006, 3:40:17 PM11/20/06
to
Dave,
I'll assume you are powering the cFP-AO-200 module with a 24V power supply. Use the same power supply to power the MFC. (Supply+, Supply -) Run the wires directly from the supply to the MFC. Do not daisy chain the MFC and the cFP-AO-200. Make sure that your supply has the capacity to run everything. The "hot wire" and valve in the MFC will require more current than most 4-20ma instruments. Wire the "out" of the cFP channel to the "setpoint" input of the MFC.
I'll assume you are powering the cFP-AO-200 module with a 24V power supply. Use the same power supply to power the MFC. (Supply+, Supply -) Run the wires directly from the supply to the MFC. Do not daisy chain the MFC and the cFP-AO-200. Make sure that your supply has the capacity to run everything. The "hot wire" and valve in the MFC will require more current than most 4-20ma instruments. Wire the "out" of the cFP channel to the "setpoint" input of the MFC.
centerbolt
Nov 21, 2006, 10:10:20 AM11/21/06
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Dave,
1. If I connect as above, will this cause problems with my other devices? They have to draw their current from somewhere and wiring it up as above wouldn't all the current for the devices in the module will have to pass through the Sierra MFC? -
I don't think you understood my answer. You need to run a separate Supply +,- from the 24V power supply to each MFC and to any other devices that are not loop powered. That includes the cFP-AO-200. It's sometimes refered to as a "star configuration". The power supply is in the middle and each device has a dedicated power feed/return directly from the supply. That means that the only power running through the cFP module is what is required to power the output signals on the "out" terminals. The return side of the output signals is already wired via the "Supply -" signal that is wired to all these devices.
Are any of your devices "loop powered"? If so, let me know what they are. Connections to those are just a pair of wires from the cFP module to the device.
2. I have two more of these MFCs for phase two of the project. Will they interfere with each other if I connect them to the same FP module? I have a 5A supply so I don't think lack of current will be an issue. I just don't want to inadvertantly cause a short or have the devices feedback through each other. -
No. The MFCs will not interfere with each other and you don't need to worry about feedback. With the cFP module and the MFC's sourced from the same power supply all the outputs and inputs of the devices are now referenced to each other via the common "Supply -" signal. The "star configuration" controls where all the different currents are flowing and keeps the cFP module from having to carry any more current than is necessary.
hope this helps
1. If I connect as above, will this cause problems with my other devices? They have to draw their current from somewhere and wiring it up as above wouldn't all the current for the devices in the module will have to pass through the Sierra MFC? -
I don't think you understood my answer. You need to run a separate Supply +,- from the 24V power supply to each MFC and to any other devices that are not loop powered. That includes the cFP-AO-200. It's sometimes refered to as a "star configuration". The power supply is in the middle and each device has a dedicated power feed/return directly from the supply. That means that the only power running through the cFP module is what is required to power the output signals on the "out" terminals. The return side of the output signals is already wired via the "Supply -" signal that is wired to all these devices.
Are any of your devices "loop powered"? If so, let me know what they are. Connections to those are just a pair of wires from the cFP module to the device.
2. I have two more of these MFCs for phase two of the project. Will they interfere with each other if I connect them to the same FP module? I have a 5A supply so I don't think lack of current will be an issue. I just don't want to inadvertantly cause a short or have the devices feedback through each other. -
No. The MFCs will not interfere with each other and you don't need to worry about feedback. With the cFP module and the MFC's sourced from the same power supply all the outputs and inputs of the devices are now referenced to each other via the common "Supply -" signal. The "star configuration" controls where all the different currents are flowing and keeps the cFP module from having to carry any more current than is necessary.
hope this helps
Little Dave
Nov 21, 2006, 10:40:21 AM11/21/06
to
Ah! Gotcha. You're right I did misunderstand your initial post. That explanation clears things up and makes sense.
There are some loop powered devices (MFCs and control valve actuators) so I will connect them as you explained above.
Thanks for the help!
DaveMessage Edited by Little Dave on 11-21-2006 09:17 AM
There are some loop powered devices (MFCs and control valve actuators) so I will connect them as you explained above.
Thanks for the help!
DaveMessage Edited by Little Dave on 11-21-2006 09:17 AM
Little Dave
Nov 24, 2006, 10:40:14 AM11/24/06
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Just a quick follow up. I wired everything up as instructed earlier in this thread and everything works well so far.
Thanks for your help, Centerbolt.
Dave
Thanks for your help, Centerbolt.
Dave
centerbolt
Nov 27, 2006, 8:40:18 AM11/27/06
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Dave,
:smileyvery-happy: Glad I was able to help. Thank you for the follow up.
It's always nice to know how things turned out.
Wayne
:smileyvery-happy: Glad I was able to help. Thank you for the follow up.
It's always nice to know how things turned out.
Wayne
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