Lone Oak (Customer) asked a question.
How to control fan speed based on static pressure?
I have a 20hp dust collector on a gs series VFD with brx series plc. I would like to have a sensor monitor the amount of suction/cfm and adjust the fan speed to maintain a certain level depending on how much dust or how many blast gates are open. I think a pitot tube with DPTA-20-15B hooked up should get me the analog signal to the plc. (is this correct?) Looking for an example or explanation on what the ladder logic, or program control would look like to make this work.
Thank you,
Joe
Never done it but sounds like an application using PID.
In poultry houses it is simply if vacuum equal which fans. With an analog signal simply compare value level to open which gates you need.
Hi @Lone Oak (Customer)
Yes, you are correct in the configuration.
https://sensoscientific.com/differential-pressure-sensors-and-monitoring-for-hvac-systems/
You would need to use the analog input to the BRX.
https://accautomation.ca/brx-plc-analog-io-system-configuration/
The compare instruction would then be used to control the fans.
https://accautomation.ca/brx-plc-compare-instructions/
Regards,
Garry
The BRX series is available here:
https://accautomation.ca/series/brx-do-more-plc/
You can use PID.
Setpoint will be your required Diff Pressure.
Your variable will be your analog input coming from your DP sensor.
And the PID output will be the your Analog output going to your VFD.
You can also set an alarm on how much maximum speed suitable to your VFD.
I'm having a hard time getting my mind around PID. I'm sure its simple once I figure it out. So if my Diff Pressure is lets say -3.6 inches water column. If I want to maintain 3.6 and have the VFD change anywhere between 40 and 60 Hz. What does the ladder logic looks like for that? I assume WX is scaled from 4-20mA (the sensor I have reads -15 to +15 water column) So if I scale it -15 to +15, I would make my SP -3.6? Then I need WY to have and out put between 40 and 60 in order to have the VFD be adjusted between? Most of the info I have found online use a discrete output rather than analog output. I think that is where I am having trouble. Being as the fan will be turned on manually. Just need the speed controlled after it is on.
Thanks for the help.
Joe
Hi @Lone Oak (Customer)
Here is a post on using the PID function in the BRX controller.
https://accautomation.ca/brx-plc-pid-with-pwm-output/
It uses a digital output, but you would just use the analog output instead.
I hope this helps you out.
Regards,
Garry
https://accautomation.ca/series/brx-do-more-plc/
Garry,
When I try to put the analog output wy0 into the timeprop structure it will only allow discrete outputs. Any thoughts on this?
Thanks, Joe
I was able to get analog output by scaling to .output% in the PID structure. I'm having trouble getting the correct scaling however. I would like my minimum Hz on the VFD to be 30 and maximum 60. At 30Hz I get lets say -2.3 for my Rx1 reading. With 60Hz lets say -6.2 Rx1 reading. If I want to maintain an Rx1 reading of -3.1, I'm not sure how that looks as far as the logic to control the Hz.
Hi Joe,
The example I did use time proportional control. You would just use the analog output of the PID.
Regards,
Garry
Hi Joe,
Take a look at the help file in the Do-more Designer Software for the PID instruction. This will show you how to scale the input and the output values to the requirements that you want.
Regards,
Garry
Enabling the Scale to .PV option will scale the raw input value to engineering units before it's used as the Process Variable (.PV). This calculation is made in both Automatic and Manual modes.
From Raw PV is the location where the raw version of the Process Variable (.PV) is stored. This can be any readable numeric location but is typically a raw analog input location (WX).
Raw Min is the minimum raw data point to use in the scaling algorithm. This can be any constant value or any readable numeric location.
Raw Max is the maximum raw data point to use in the scaling algorithm. This can be any constant value or any readable numeric location.
Eng Min is the engineering data point that equates to the Raw Min parameter value to use in the scaling algorithm. This can be any constant value or any readable numeric location.
Eng Max is the engineering data point that equates to the Raw Max parameter value to use in the scaling algorithm. This can be any constant value or any readable numeric location.
Eng Units is an 8 character string that will be displayed on the PID View. This can be a String Literal Zero or more characters enclosed in double-quotes, as in "hello", and may include both simple escape sequences (such as \t for the tab character) and hexadecimal data (such as 0xAA). any of the system-defined Short Strings, or system-defined Long Strings, or user-defined Strings.
Scale from . Output % enables optional scaling of the Output value (.Output) before it's stored in the designated analog output location. The raw. Output value has a range of 0.0 to 100.0. This calculation is made in both Automatic and Manual modes.
Scaled Min is the minimum scaled value to use in the scaling algorithm corresponding to when.Output value equals 0.0. This can be any constant value or any readable numeric location.
Scaled Max is the maximum scaled value to use in the scaling algorithm corresponding to when. Output value equals 100.0. This can be any constant value or any readable numeric location.
To Scaled is the output location to store the scaled Output value. This can be any writable numeric location but is typically a raw analog output value (WY). Note: because this scale calculation is made in Manual mode, you cannot write directly to the To Scaled location; you must write to the PID loop. Output structure member which will then get reflected in the calculated To Scaled value.