ptonsparky
Tom
- Occupation
- EC - retired
The objectives were there, just deeper into the plot.I thought this was simple at first - as long as Fi > Fo you should never run the tank empty, but then you added more objectives:
Math: If Train A leaves the station traveling...
- Thread starter ptonsparky
- Start date
- Status
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180511-1454 EDT
ptonsparky:
Assuming your PLC can control the input feed rate, then you may be able to automatically adjust that feed rate to achieve a nearly constant level.
Assume a priori that you approximately know the needed input feed rate. Start with that feed rate plus a little bit.
This will get you to the full point (limit switch). At the full point slow to possibly 3/4 of what you believe is the output flow rate. This will cause the tank to drain.
Allow this draining to occur for possibly 15 to 30 seconds. Then go back to the slightly faster input rate than output rate, and determine how long to get back to the full limit. Your algorithm that you create that uses this information can adjust the values for a better solution for the rate and time values.
Include a time override that if full is not achieved in some reasonable time that feed rate is increased to correct the temporary problem.
A lot of factors may determine how factors are selected or limited.
However, you create an algorithm its basic function is to servo about the single on-off threshold (limit switch or whatever) in such a way as to practically control the tank level to a minimum variation. This is still a "bang-bang" servo, but without full on and full off.
Possibly a proportional level sensor might be useful, or an on-off wide area averaging sensor.
.
ptonsparky:
Assuming your PLC can control the input feed rate, then you may be able to automatically adjust that feed rate to achieve a nearly constant level.
Assume a priori that you approximately know the needed input feed rate. Start with that feed rate plus a little bit.
This will get you to the full point (limit switch). At the full point slow to possibly 3/4 of what you believe is the output flow rate. This will cause the tank to drain.
Allow this draining to occur for possibly 15 to 30 seconds. Then go back to the slightly faster input rate than output rate, and determine how long to get back to the full limit. Your algorithm that you create that uses this information can adjust the values for a better solution for the rate and time values.
Include a time override that if full is not achieved in some reasonable time that feed rate is increased to correct the temporary problem.
A lot of factors may determine how factors are selected or limited.
However, you create an algorithm its basic function is to servo about the single on-off threshold (limit switch or whatever) in such a way as to practically control the tank level to a minimum variation. This is still a "bang-bang" servo, but without full on and full off.
Possibly a proportional level sensor might be useful, or an on-off wide area averaging sensor.
.
kwired
Electron manager
- Location
- NE Nebraska
ptonsparky
Tom
- Occupation
- EC - retired
I couldn’t talk them into the proportional control.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180512-1544 EDT
ptonsparky:
Expanding on my post #42 of yesterday.
I believe my suggestion of that post can reduce your level variation, min max level vs time, by some substantial value if the method has no impact on your loss of steam problem.
Some assumptions:
1. The single point level sensor has no inherent hysteresis at its threshold level point, and that its ability to sense the average tank level at that threshold is a small fraction of the min to max level variation achieved with your present 3 minute no input feed time method (full on-off control of the input feed rate). Mechanical hysteresis would be no problem, but is not required.
2. By my two input feed rate method there is no increase in the steam loss problem.
3. By using the PLC to switch the input feed rate between two rates has no effect on the lifetime of the equipment. Thus, fast slow cycling can be a shirt time cycle.
4. Feed rates specified by the PLC are close to the actual process feed rates. May not matter too much, but probably. can be monitored by the activity of the level threshold sensor activity.
5. Separate means are included in the PLC to protect from abnormal conditions.
This system can be made to servo from your programmed output feed rate by simple delta values used to create the fast and slow input feed rates. Thus, a single value can be adjusted to determine cooking time.
If there is short time oscillation of the output of the level threshold sensor at the sensing point, then some amount of on or off or both time delay may be required from the sensor. In other words a low pass filter. This creates a type of hysteresis based on time rather than level.
.
ptonsparky:
Expanding on my post #42 of yesterday.
I believe my suggestion of that post can reduce your level variation, min max level vs time, by some substantial value if the method has no impact on your loss of steam problem.
Some assumptions:
1. The single point level sensor has no inherent hysteresis at its threshold level point, and that its ability to sense the average tank level at that threshold is a small fraction of the min to max level variation achieved with your present 3 minute no input feed time method (full on-off control of the input feed rate). Mechanical hysteresis would be no problem, but is not required.
2. By my two input feed rate method there is no increase in the steam loss problem.
3. By using the PLC to switch the input feed rate between two rates has no effect on the lifetime of the equipment. Thus, fast slow cycling can be a shirt time cycle.
4. Feed rates specified by the PLC are close to the actual process feed rates. May not matter too much, but probably. can be monitored by the activity of the level threshold sensor activity.
5. Separate means are included in the PLC to protect from abnormal conditions.
This system can be made to servo from your programmed output feed rate by simple delta values used to create the fast and slow input feed rates. Thus, a single value can be adjusted to determine cooking time.
If there is short time oscillation of the output of the level threshold sensor at the sensing point, then some amount of on or off or both time delay may be required from the sensor. In other words a low pass filter. This creates a type of hysteresis based on time rather than level.
.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Your two speed scheme has the potential to reduce motor starts significantly. And VFD action makes each start less stressful to the motor.
using this you can select starts per hour
Vi/Vo = t/(t-3)
assume you want 4 per hr
run time = 60/4 = 15 minutes
Vi/Vo = 15/(15-3) = 1.25
assume: Vi = 12.5 and Vo = 10
product per cycle ~ Vx x run time
in = 12.5 x (15-3) = 150
out = 10 x 15 = 150
net = 0 so level delta = 0
Vi/Vo = t/(t-3)
assume you want 4 per hr
run time = 60/4 = 15 minutes
Vi/Vo = 15/(15-3) = 1.25
assume: Vi = 12.5 and Vo = 10
product per cycle ~ Vx x run time
in = 12.5 x (15-3) = 150
out = 10 x 15 = 150
net = 0 so level delta = 0
ptonsparky
Tom
- Occupation
- EC - retired
As it sits now, unless suppliers of the other equipment change their process, the VFD min speed is the 46 HZ.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
`180512-2408 EDT
Where does 46 Hz come from? This is the first I have seen it mentioned. What does it apply to --- both input and output drives, or just one of them?
Why cam't 46 Hz be lower?
How do input and output Hzs relate to input and output feed rates, and the feed rates you need to operate at?
.
Where does 46 Hz come from? This is the first I have seen it mentioned. What does it apply to --- both input and output drives, or just one of them?
Why cam't 46 Hz be lower?
How do input and output Hzs relate to input and output feed rates, and the feed rates you need to operate at?
.
ptonsparky
Tom
- Occupation
- EC - retired
My post #39, the graph, shows a green line indicating the VFD requested HZ. That is for the incoming product. The out going product is via manual speed control of DC motors.
Other equipment must sense the incoming product and it can’t do that at less than 46 HZ of my VFD.
My first design of this system included two speeds for the VFD, as has been suggested,with thoughts that I could get the PLC logic to adjust the lower operational HZ once the DC motors were at speed. The other equipment limits made that plan obsolete.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
180513-1516 EDT
ptonsparky:
What happens if you change the 3 minute timer to 30 seconds, or even 15 seconds?
.
ptonsparky:
What happens if you change the 3 minute timer to 30 seconds, or even 15 seconds?
.
ptonsparky
Tom
- Occupation
- EC - retired
- Status