LOAD RPM

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Yes. We monitor the driven end. Four count per revolution. Updated RPM display every 10 seconds.
Something to watch out for is the algorithm used to calculate RPM in such a system.

A really simple approach is to simply count up the number of pulses per unit time. The problem is that the number of pulses is always an integer, which means you will be high or low by a fraction of a pulse. In your system, 200 pulses in a sampling period would mean 300 RPM, 199 pulses would mean 298.5 RPM, and any speed between those that correspond to integral pulse counts will 'flicker' between the allowed values. This can cause problems if your alarm values are too tight.

-Jon
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Something to watch out for is the algorithm used to calculate RPM in such a system.

A really simple approach is to simply count up the number of pulses per unit time. The problem is that the number of pulses is always an integer, which means you will be high or low by a fraction of a pulse. In your system, 200 pulses in a sampling period would mean 300 RPM, 199 pulses would mean 298.5 RPM, and any speed between those that correspond to integral pulse counts will 'flicker' between the allowed values. This can cause problems if your alarm values are too tight.

-Jon
The 10 and 20 % values we use for legs were fairly easy. 2.7% could get touchy. I do have an adjustable delay built in. At this time I don’t necessarily need to stop any thing at that point, but I do need to flag the problem area. I don’t see the millwrights making any changes unless we can tell them what and where it is happening.

Waiting for weather to clear up. Everything is in the rain right now.
 

kwired

Electron manager
Location
NE Nebraska
The advantage of monitoring driven load speed is you catch change in speed of the actual working component if say a drive belt or other drive component would be slipping but drive motor doesn't slow down.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Went there today. The only auger motor that I do not monitor for rpm or current, the auger was stuck. Burned some belts for a bit. I blamed it on rain soaked corn that swelled in the auger. The millwrights haven’t gotten around to covering that 24” hole in the top of the bin. 4-5” of rain in the last few days.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Chalking the perimeter of the machine they just set. People would assume that the lines were there first and that the machine was perfectly positioned by said millwrights.
Gee... that would be like wiring something up so that it works, then going back and making schematics for it so that it looks like you wired it up per the drawings. I've never done that... 😇
 

kwired

Electron manager
Location
NE Nebraska
Gee... that would be like wiring something up so that it works, then going back and making schematics for it so that it looks like you wired it up per the drawings. I've never done that... 😇
I've often drawn schematics before building something, then finding out something doesn't work as planned or needs tweaking or other changes, then have to change the drawing afterwards.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Got to run it. Captured the high currents at pin shear. Isolated where the problem area is and politely as I could told the millwright “It’s not electrical.”

By charts, the input is 200 BPH more of Dry corn than one of the other augers can handle. That and it’s milled by then. Not near as smooth and free flowing. Plus the extra moisture content, no bin cap, made it worse.
 

retirede

Senior Member
Location
Illinois
Got to run it. Captured the high currents at pin shear. Isolated where the problem area is and politely as I could told the millwright “It’s not electrical.”

By charts, the input is 200 BPH more of Dry corn than one of the other augers can handle. That and it’s milled by then. Not near as smooth and free flowing. Plus the extra moisture content, no bin cap, made it worse.
Milled corn will have a higher density than shelled corn as well, I would think.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
29898.jpeg

Shows the Mill was at 80+ amps and the auger amps at 50+ amps when the counter on the mill detected less than 1 count in 2 seconds. Auger should have been about 9 amps. The auger is able to clear soon after the mill stops. You can see it is running empty at this time. Four shear bolts were in place instead of the normal two. They held but the rpm dropped to below limits.
 

paulengr

Senior Member
210311-0809 EST

ptonsparky:

Your suspicion is wrong unless the motor is a synchronous AC motor inherently.

A DC permanent magnet or fixed field motor is approximately a straight line with respect to torque load.
A series wound DC motor, armature is in series with field, has a very nonlinear curve. High torque at zero speed.

An AC induction motor is a more nonlinear speed torque relationship. Usually has a foldback characteristic.

.
In the normal operating range (not accelerating) speed/torque is almost linear up to around 2-3x name plate torque. A useful approximation to measure torque is look at the name plate speed and measure RPM. So if the name plate says 1760 and it’s turning at 1780 then knowing synchronous is 1800 we know torque is about 50%. If it’s at 1740 torque is at 150%. Not exact but pretty close. It only gets very nonlinear at close to breakdown torque.
 

paulengr

Senior Member
There is a reason to call electricians. An electrician pulls up and might spend all day trying to find what’s wrong then 5 minutes to fix it.

As soon as a mechanic has to troubleshoot something more complicated than yep it broke in half and is laying on the ground in pieces, they’re done. If it’s obvious like that they take all day to fix it. They think a neutral means the gear in the truck that you use only when you need to pop the clutch. Overload means spray some belt dressing on it, give it two shots of grease and slam the breaker handle hard enough it snaps off so it won’t keep tripping for no good reason. And jamming means you need to cut half of whatever is jamming off so it turns better. But when the smoke comes out of the motor or the fuses blow in half that means the motor was defective or the starter is too weak to hold everything in like it should. Ground is where your dropped tools end up. Grounding is when you take the keys away from your teenage kids. Conduit is for tying ropes and chains to in order to pull stuff. Too bad electricians don’t know how to build things good and strong like mechanics. Breakers are there to make stuff stop working so operators can get a break when they need one. Fuses are just an expensive nuisance that old timers use instead of breakers. Takes longer to run up to the feed and seed to get more. Copper plumbing works much better if you want the operator to just keep working and not interfere with nap time. A circuit is what electricians do when they go from box to box trying to figure out what is wrong. A Volt is a car model. An amp is for making electric guitars work. And electricians are people mechanics tolerate because they give your brain a chance to rest while they figure out what is wrong for you while you take a break and go get a drink.

So that’s why most people call an electrician first.
 

ValeoBill

Member
Location
Wasaga Beach, Ontario
Occupation
Industrial Electrician
There is a reason to call electricians. An electrician pulls up and might spend all day trying to find what’s wrong then 5 minutes to fix it.

As soon as a mechanic has to troubleshoot something more complicated than yep it broke in half and is laying on the ground in pieces, they’re done. If it’s obvious like that they take all day to fix it. They think a neutral means the gear in the truck that you use only when you need to pop the clutch. Overload means spray some belt dressing on it, give it two shots of grease and slam the breaker handle hard enough it snaps off so it won’t keep tripping for no good reason. And jamming means you need to cut half of whatever is jamming off so it turns better. But when the smoke comes out of the motor or the fuses blow in half that means the motor was defective or the starter is too weak to hold everything in like it should. Ground is where your dropped tools end up. Grounding is when you take the keys away from your teenage kids. Conduit is for tying ropes and chains to in order to pull stuff. Too bad electricians don’t know how to build things good and strong like mechanics. Breakers are there to make stuff stop working so operators can get a break when they need one. Fuses are just an expensive nuisance that old timers use instead of breakers. Takes longer to run up to the feed and seed to get more. Copper plumbing works much better if you want the operator to just keep working and not interfere with nap time. A circuit is what electricians do when they go from box to box trying to figure out what is wrong. A Volt is a car model. An amp is for making electric guitars work. And electricians are people mechanics tolerate because they give your brain a chance to rest while they figure out what is wrong for you while you take a break and go get a drink.

So that’s why most people call an electrician first.
We've never met Paul but it appears we've worked with the same mechanics ! ....great response
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Milled corn will have a higher density than shelled corn as well, I would think.
Interesting geometric tidbit: Some people feel intuitively that smaller objects should pack better. But in fact if the shape is unchanged objects of any uniform size will have the same packing fraction (ratio of occupied space to total space.)
Milled corn can have a higher density than shelled corn for three reasons.
1. The shape of milled corn particles allows tighter packing than shelled corn particles.
2. Milled corn contains a mixture of particle sizes, allowing the smaller ones to fit into the voids between the larger pieces.
3. Milled cord particles are softer and so can be packed tighter because the touching parts can compress to allow closer packing.
 

retirede

Senior Member
Location
Illinois
Interesting geometric tidbit: Some people feel intuitively that smaller objects should pack better. But in fact if the shape is unchanged objects of any uniform size will have the same packing fraction (ratio of occupied space to total space.)
Milled corn can have a higher density than shelled corn for three reasons.
1. The shape of milled corn particles allows tighter packing than shelled corn particles.
2. Milled corn contains a mixture of particle sizes, allowing the smaller ones to fit into the voids between the larger pieces.
3. Milled cord particles are softer and so can be packed tighter because the touching parts can compress to allow closer packing.
Exactly. Depending on the characteristics of the mill, a good percentage of the corn ends up almost like powder, which fills the gaps nicely.
 
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