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Controlling an analogue output based on analogue input

Created by: nathan_hewitt22 at: 1/22/2025 9:45 AM (6 Replies)

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1/22/2025 9:45 AM	Rate (0)
nathan_hewitt22 Joined: 1/22/2024 Last visit: 1/24/2025 Posts: 13 Rating: (0)	Hi, hope someone can assist. I am looking for the correct block program arrangement for controlling an analogue output based on an analogue input. I need to maintain a constant current by varying the voltage. Current signal will be 0-10v analogue via hall effect sensor and the voltage control will be via an analogue 0-10v phase angle controller. I know this seems simple, but the current is continuously varying (based on changes in resistance) and the voltage will need to be continuously adjusted up and down accordingly. I should be able to work this out, but just can't find the right blocks. Would also be good to be able to set the current value via a TDE module or the webserver. Also need to be able to send a alert signal when the current falls below a set point- i.e. voltage cannot be raised far enough to maintain current, but that bit should be easy. Any advice would be appreciated. Nathan

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1/22/2025 11:58 AM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 1/24/2025 Posts: 34557 Rating: (4313)	You should describe more. The analog input signal: Signal increases > increase current? or Signal decreases > increase current? What physical measuring range does the analog input signal correspond to? 0V - 10V = 0 - ??? A? What physical measuring range does the analog output signal correspond to? 0V - 10V = 0 - ??? A?

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1/22/2025 7:32 PM	Rate (0)
nathan_hewitt22 Joined: 1/22/2024 Last visit: 1/24/2025 Posts: 13 Rating: (0)	Many thanks for quick reply. So the objective is to maintain current at 16A. Lets say for the analogue input (system current) 0A system current is 0V analogue input and 32A system current is 10V analogue input. For the analogue output (system voltage), 0V system voltage is 0V analogue output and 110V system voltage is 10V analogue output. If the system current drops below 16A (less than 5V analogue input), the system voltage must be increased from 55V (higher than 5V analogue output) until it comes back up to 16A (5V analogue input). Equally, the system current may rise above 16A (greater than 5V analogue input) and the system voltage must be reduced below 55v (below 5V analogue output). Lets also say a 10% deviation in system current is acceptable to avoid changes running to infinity. Hope that makes sense.

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1/22/2025 8:15 PM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 1/24/2025 Posts: 34557 Rating: (4313)	Something like this? Attachment Controlling_current_0BA8.Standard.zip (6 Downloads)

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1/23/2025 7:39 AM	Rate (0)
nathan_hewitt22 Joined: 1/22/2024 Last visit: 1/24/2025 Posts: 13 Rating: (0)	Wow, that's spot on. Seems it was a little more complex than I thought (for me anyway)! Just need a way of adjusting the required current. I think I will do that by inserting multiple mathematical function blocks that can be turned on and off via the buttons on the TDE/website. Many thanks for your help!

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1/23/2025 7:50 AM	Rate (0)
ixo65 Grandmaster-Expert Joined: 12/18/2014 Last visit: 1/24/2025 Posts: 34557 Rating: (4313)	nathan_hewitt22 Wow, that's spot on. Seems it was a little more complex than I thought (for me anyway)! Just need a way of adjusting the required current. I think I will do that by inserting multiple mathematical function blocks that can be turned on and off via the buttons on the TDE/website. Many thanks for your help! Now I'm a bit confused. You write that my suggestion does exactly what you imagined. But you still don't want to use it. Why? It's nothing complicated, it's just a simple linear equation....

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1/23/2025 8:42 AM	Rate (0)
nathan_hewitt22 Joined: 1/22/2024 Last visit: 1/24/2025 Posts: 13 Rating: (0)	Ahh sorry, I didn't explain that properly. I will definitely be using your program! To give some background, this will be controlling an electrocoagulation system for treatment of waste water. The effectiveness of the system is relative to the current density across the surface of the plates, which has to be kept constant as the resistance of the waste stream fluctuates (and as the distance between plates increases due to electrode surface loss)- hence your program. However, one installation may require a current density of 16A across the plates, while a scenario with higher pollutant level may require say 25A across the plates. Your program is set up to maintain 16A, but I need to be able to adjust that set current up and down manually as required to obtain the sweet spot during set up. Another variable is water flow rate and this can easily be varied with an analogue output to a speed controller set manually (or even varied automatically according to output from a water analysis probe). It may be that I decide to set the current density high and then find the sweet spot for water clarity using water flow rate. There are other variables too that affect the efficiency, such as pH of the effluent that may influence required current density.

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