"bang bang" effect on tractor hydraulics.

[BertZegers]

There is always more than one way to "skin a cat" - and in this case, it would be the CONTROLLER that determines how much extra wear and tear your hydraulics would see - if you already have a specific controller in mind, pics and links would be useful... Steve

I am using a machine level laser and laser receiver for input in a PLC. The PLC controls the electric hydraulic valves. It is a experimental setup. I think the programmable timers in the PLC will make it workable. It will act every second.

If it works I will post!

My worry is that the electric valves cause a spike in the hydraulics that might be damaging. I am aware of electric valves being used in tractors all the time. But I also know that there are a thousand different models, and for a reason. Is there a type of valve that mitigates spikes?
I am a electrician by trade, but have only basic knowledge of hydraulics, so every help is welcome.

 

[PhysAssist]

I am using a machine level laser and laser receiver for input in a PLC. The PLC controls the electric hydraulic valves. It is a experimental setup. I think the programmable timers in the PLC will make it workable. It will act every second.

If it works I will post!

My worry is that the electric valves cause a spike in the hydraulics that might be damaging. I am aware of electric valves being used in tractors all the time. But I also know that there are a thousand different models, and for a reason. Is there a type of valve that mitigates spikes?
I am a electrician by trade, but have only basic knowledge of hydraulics, so every help is welcome.

I don't want to speak for him, but you might could drop a PM to J_J as he has helped many of us with hydraulic questions over the years.

Just sayin,
Thomas

 

[muddstopper]

I dont know how what your trying to use is supposed to work, but my experiences with computer controlled hydraulics, (operation, not designing,), is That the solenoid valves are nothing special. I know of several pieces of equipment that have been upgraded to computer control that had previously been all manual control without any changes to the hydraulic system. The solenoid sees a electric signal whether you hit a toggle switch, push button or foot pedal, or the computer is sending the signal. I also know that some valves use a hydraulic solenoid valve at low pressure to send hydraulic fluid to another valve that moves a spool that sends system pressure thru yet another valve. I dont think you are going to see that kind of hydraulic system on a tractor, at least not a small tractor. Now one of those 500hp, track drive, tractors that pulls a 25row plow, they might have all sorts of valves in their systems. Your tractor hydraulics have a safe load rating that is controlled with reliefs. Any pressure spikes should be taken care of by the excess pressure dumping over the relief. I think your biggest problem might be the constant forward and reversing of oil flow might cause excessive heat and might require some sort of oil cooler to keep the oil from heating up.

 

[BertZegers]

Thanks Muddstopper, for your expert advice. I will watch the heat.

 

[BukitCase]

Hey Bert, that helps me see where you're coming from - I retired a couple years ago after spending the last 35 years in rare metals plants as Instrumentation/controls tech. In Oregon that required TWO electrical licenses (mostly for "revenue enhancement" IMO) -

After I posted, I googled "tractor hydraulic laser level control", and partially confirmed one of my concerns - one unit brags about doing SIX corrections per SECOND. My concern on that is - a human may make maybe a little over 1 correction per second if they're really watching, but 6/sec. = 360/minute, so whatever pulsation occurs with an on-off cycle at FULL PRESSURE, happens 21,600 times per hour of use.

I have seen improperly tuned valve controllers (electric over pneumatic) DESTROY a $5000 valve in a few HOURS because of incorrect "tuning" of the PID loop; speaking of which, you haven't yet mentioned whether the PLC you're playing with (NOT a derogatory term in MY world) is "far enough up the food chain" to have PID modules available for control or just "bang-bang" outputs - but if you have PID options I may be able to find a basic tuning guide that would get you in the ball park.

The trick (besides understanding PID control) is to find a compromise tuning that will be fast enough to keep the "process" happy but SLOW enough to maximise MTBF of the equipment.

Depending on how rugged the topography of your target surface is to begin with, that "trick" may get tricky indeed ... Steve

 

[k0ua]

Hey Bert, that helps me see where you're coming from - I retired a couple years ago after spending the last 35 years in rare metals plants as Instrumentation/controls tech. In Oregon that required TWO electrical licenses (mostly for "revenue enhancement" IMO) -

After I posted, I googled "tractor hydraulic laser level control", and partially confirmed one of my concerns - one unit brags about doing SIX corrections per SECOND. My concern on that is - a human may make maybe a little over 1 correction per second if they're really watching, but 6/sec. = 360/minute, so whatever pulsation occurs with an on-off cycle at FULL PRESSURE, happens 21,600 times per hour of use.

I have seen improperly tuned valve controllers (electric over pneumatic) DESTROY a $5000 valve in a few HOURS because of incorrect "tuning" of the PID loop; speaking of which, you haven't yet mentioned whether the PLC you're playing with (NOT a derogatory term in MY world) is "far enough up the food chain" to have PID modules available for control or just "bang-bang" outputs - but if you have PID options I may be able to find a basic tuning guide that would get you in the ball park.

The trick (besides understanding PID control) is to find a compromise tuning that will be fast enough to keep the "process" happy but SLOW enough to maximise MTBF of the equipment.

Depending on how rugged the topography of your target surface is to begin with, that "trick" may get tricky indeed ... Steve

Hmmm.. Starting to understand more also... Um what is the "throw time" of the solenoid? Can it even make 6 transitions per second? or even anywhere near that? I am questioning now whether these valves are even what you want. I don't have any experience in this field, but I do have a good understanding of basic electronics, fly time of relays and solenoids etc. Low mass relays move a heck of a lot faster than big old high mass chunks of metal.

 

[BukitCase]

Good point James - speaking of "big clunky things", what about moving a 1300 pound box blade that fast??!?

I would hope that the company who claimed 6 corrections/sec. is more honorable than (for example) Coleman, who would have you believe that their 120 volt "homeowner" air compressor is 6 horsepower

Do the math on THAT one, then tell me where to find a 40 amp receptacle for 120 volts ... Steve

 

[RDrancher]

You may want to talk to member Completelawncare. He has a setup for doing sports fields. Here's a thread http://www.tractorbynet.com/forums/projects/338834-laser-grading-football-field.html. Member Jenkinsph is also working on a setup and may chime in.

 

[BukitCase]

Good advice - theory may be fun (for some), but nothing beats "BTDT, got the tee shirt"... Steve

 

[oldnslo]

Companies like Spectra Physics have been doing this for more than 15 years. You just need to select components that will handle the duty cyce being asked of them. Solenoid valves can shift in 100 milliseconds or less depending on design, flow rate, pressure, etc.