We’ll be using the exact same hardware that we used in all of the WEG CFW100 and CFW300
PID videos so if you’ve seen any of those videos this is going to look real familiar
with just a couple changes. We have a single phase 220-volt input, 1 horse
power WEG CFW500 drive, controlling this Jet Pump Motor. The motor is connected to a swimming
pool pump that pulls water from a reservoir and sends it up to these nozzles which we
can turn on and off. The water then drains back to the reservoir.
The pressure is monitored using this 15-psi sensor which sends a zero to 10-volt signal
back to the drive. We’re using an external switch to control
run stop and another switch to switch PID’s between automatic and manual modes.
Finally, we’ll be using the optional alphanumeric remote keypad to operate and monitor PID because
it makes everything easier to see. This is the wiring diagram. You can download
a copy of that and these other diagrams at the links in the description below the video.
Notice I’m using the drives built-in 24-volt supply to power both the remote HMI and the
sensor. I love that I don’t have to buy and find space for a separate power supply.
Just be careful you don’t exceed the 150-mA limit of the 24-volt supply. These each draw
less than 20mA so we are in great shape. The other thing to notice is that I am using
a NEMA-4X drive with a built-in disconnect. Again, another thing I don’t have to buy,
mount, wire and make sure it meets the NEMA-4X spec. That’s awesome!
I’ve included the AutomationDirect part numbers for all the components used - including the
selector switches and the sensor’s quick disconnect cable.
I’m using the option module that comes pre-installed in the drive. If you order it separately,
it goes by this part number. If you are using a different option module these pin numbers
may be different. Here it is. Again, this NEMA-4X drive with
built-in disconnect is controlling this motor and pump which pulls water in from the reservoir
– which you can’t see here - and sends it up, to the nozzles which we can turn on
and shut off using these valves. The water drains out the back of the tank into the reservoir.
This sensor sends the pressure reading back to the drive using a 0-10-volt signal. The
sensor is mounted at the bottom of a stanchion pipe to minimize noise. You can learn about
that in this video. Finally, we’re using the optional alphanumeric
HMI display to monitor and control the process and these selector switches to control run
stop and PID auto/manual modes. Let’s zoom in on the HMI and switches and make everything
easier to see and leave space for notes. The drive has been reset to factory default
and I already entered the basic motor parameters and configured the remote HMI. These videos
show you how to do both of those so I won’t take the time to explain that here.
If I hit Run and speed up the motor to say 40 Hz, sure enough water shoots out any nozzle
that I open a valve for. Of course, each time I open a valve, the system pressure is going
to drop a little. How much? Let’s use this line of the display to monitor the pressure
sensor that’s coming in on analog input 1.
Let’s go to Parameter 206 which controls the 2nd line of the display and tell it to
monitor Parameter 18 which is the analog input 1 value in percent of full scale.
Escape back to the top level and now we can see the actual system pressure in zero to
100% right here on the display. Perfect. For these videos, let’s assume we want to
maintain a system pressure of 6 psi. 6 psi is 40% of the sensor’s 15 psi so with one
valve open, I’ll adjust the motor speed until we get to 40% which is 6 psi on this
sensor. Open another valve and we see the pressure
drop. Raise the motor speed to get back to 40% or 6 psi.
Open another valve, pressure drops again. Raise the motor speed to get back to 6 psi
Open the last valve, pressure drops. Raise the motor speed again to get back to 6 psi.
And if we close the valves, we need to reduce the motor speed again to get back to 6 psi.
So we just did manually what we want PID to do for us automatically – right? Every time
the pressure changes we want PID to automatically adjust the motor speed to keep the system
pressure at 6 psi. It’s really important to notice that our
system IS capable of maintaining 6 psi regardless of how many valves are open. If we can’t
manually get the system to maintain 6 psi, then PID won’t be able to do it either.
PID isn’t magic – it can’t make your system do something it isn’t designed to
do. Ours is, so we are good to go. The other thing to notice is that there is
plenty of motor speed left over between here and 60 Hz. I call that headroom. That’s
important. PID needs that extra motor speed to make fast changes. Kind of like when you
step on the accelerator in your car to get on the highway. You mash the gas pedal like
you want to go 120 miles per hour, but then when you get close to 60 you back off. PID
does the same thing. It needs as much extra headroom as you can give it so it can accelerate
quickly to give you a quick response. Finally, we need to know one more thing. What
motor speeds give us zero and 100% of our sensor's range, which is zero to 15 psi for
our dem. So I’ll lower the motor speed until I get close to zero psi and note that.
And then raise the motor speed to the sensor's top end and record that. But that was for
1 valve. I’ll repeat that for 2 valves, note that speed … 3 valves, note that speed
… and four valves and note that speed. If we plot that out it looks like this. The
average is somewhere in here. This line is what PID uses to make all of its decisions.
So it’s really important that you know what these min and max speeds are.
We used an average here. If you want the system to be more accurate when lots of valves are
open, then you might want to move the line up here somewhere. If you want the system
to be optimized for fewer valves, then you might want to move the line to somewhere around
here. Regardless, its these two numbers over here that tell PID how to react, so make sure
you know what those are. If you can’t run your system all the way
to zero or 100% of your sensor's range, then get some intermediate numbers and extrapolate.
That will get you close enough. Great! We now know that our system CAN do
6 psi regardless of how many valves are open. We know our system has plenty of extra motor
speed head room and we know the min and max motor speeds to get the full range of our
sensor. We are now ready to implement PID. Join me
in Part 2 where I’ll show you how to simplify what can be a daunting task - keeping track
of all the PID related parameters. Using that method, we’ll have PID automatically maintaining
the system pressure for us in no time. Click here to learn more about the WEG CFW500
drive. Click here to learn about AutomationDirect’s free award-winning support options and click
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