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View Full Version : 0 to 100% or 0 to 100%, which do you use ?

PrestonPierce
01-31-2007, 08:04 PM
I was doing a start-up on a AHU, var speed discharge air control with a preheat coil and var speed exhaust. Anyway the unit/drive guy tells me while doing his start-up that I should scale my 0-10vdc signal output to coincide with his , 21hz (minimum) to 60hz ?,, result was that my 0-10 operated between 21 hz and 60 hz ? how do you guys do it,

I have only ever used my signal to represent 0 hz to 60 hz, , why would he want me to scale back to control 21 to 60 hz? besides that it screws up the percentage that I will show on graphics in R2, it causes me to do some extra math, what I usually do is take my 0-10 and limit it in the Jace with a math block = output hi and low set at 35% and 100%, then use a select block
(made program)so that when I command the unit on I show the 35% min but I don't ramp the drive up till I go over 3.5 volts, follow me ? I can see his point about having more control over the speed because I'm dividing my 100 over 39hz instead of 60 hz, but I figure its not that critical, I would rather represent the true signal at the graphics, of course if I had a reliable feedback from the drive I wouldn't have to worry about it, but I don't.

So how do you guys do it ? do you scale from the minimum hertz to 60 or scale from 0 to 60, I'm using hertz to keep it simple I realize that a lot of guys do it in speed 0 to 100 as I actually do also,

when referring to minimum it is the minimum set in the drive,

willf650
01-31-2007, 08:19 PM
I scale the drive so 0v = min drive speed and 10v= max drive speed. Min and Max drive speed aren't always the same and Max drive speed isn't alway 60HZ some times its more some times less. I'd rather have more control of the drive than a better read out on the graphics but that just me.

PrestonPierce
01-31-2007, 08:32 PM
I agree it woud be better control but I've never had a problem with hunting or maintaining a staic pressure that I coudn't solve by adjusting the loop paramaters, I am primarily working with variable speed DA control systems, that run from min hz whatever it is, ( I think 21hz is awful high for a min to begin with) to 60 hz, I realize that some may want to control to a higher or lower hertz than 60 but for my apps it is always 60 hz,

codewriter
01-31-2007, 08:51 PM
20-60 is pretty typical, at least I think so. Some guys say down to 15hz is ok, some say 18hz, some say 20hz, and some say 30hz. I say I do what the motor manufacturer will warranty under the given application.

Scaling graphics should not be a consideration for the method you choose, just use reset logic for your graphical representation of thats important to you, that way you can do what ever you want.
example:
In 0&#37; = Out 20hz
In 100% = Out 60hz
or
In 0% = Out 18hz
In 100% = Out 56hz
or...etc....

Just take your control output and use it as the in to a reset function, then take the reset output and use it for your display.

Use as much of the control band you have, dont narrow it down for graphical sake. Personally I would be using current rather than voltage as well.

PrestonPierce
01-31-2007, 09:01 PM
Yeah I can make it work like that, but I have never had a problem doing it directly, I guess I just don't see a lot of benefit to scaling it from the minimum , it doesn't seem to be a big deal on the control side of the static pressure. what ever my output is if it is below 3.5 volts I just show 35 on the graphics and the drive is at its minimum so no one ever sees the actual output signal, I have never had an air handler where I think it would have mattered much on the control of the static pressure, eventually either strategy will end up in the same place. If I were controlling something more critical than static pressure then I may consider it, but static control isn't that critical to me if I am stable and .2 either way of setpoint then it is good enough for me, this is the typical method used in this area. I was wondering what you guys do and you seem to agree with the drive guy, so I learned something.

codewriter
01-31-2007, 09:13 PM
Your either not doing jobs that require 3rd party CXA's, or the CXA's in your area are not as detailed as the ones I deal with. ~.2 from setpoint? wow, thats out there, unless your dealing with high pressure systems.

And the extra scaling is in fact a big deal. Unless your doing stop-n-go's, etc... I suggest you rethink your methods.

PrestonPierce
01-31-2007, 09:39 PM
Yeah should have said .02, not 1.3 to 1.7 on a setpoint of 1.5,
1.48 to 1.52

simsd
02-01-2007, 01:07 AM
Generally if my voltage is not doing anything below a certain point, I'll change my scale to match. ie:

2 volts = 20% = 12 HZ (just an example)

10 volts = 100% = 60 HZ.

I do it this way because I don't have to think about different translations.

This is not always possible at the controller level (adjusting the voltage range). It all depends how you think.

dingman
02-01-2007, 09:03 AM
If a VFD guy told me to scale that way, I'd just tell him no. Unless you need that extra resolution for control purposes, then there is no reason for it and as you've mentioned, it causes more grief for you and the customer and anyone coming behind you to troubleshoot it.

Nope, 0 VDC (IMO) should always be 0 Hz (zero output from the device)
and
10 VDC should be 60 Hz (100% output from the device).

dingman
02-01-2007, 09:11 AM
I agree that it's how you think of it and the way I think of it is to keep it simple. A device should always be at 50% of it's output at 50% of my signal.

I can see what you're saying though, you're thinking that your device output starts at 12Hz.

Generally if my voltage is not doing anything below a certain point, I'll change my scale to match. ie:

2 volts = 20% = 12 HZ (just an example)

10 volts = 100% = 60 HZ.

I do it this way because I don't have to think about different translations.

This is not always possible at the controller level (adjusting the voltage range). It all depends how you think.

simsd
02-01-2007, 10:57 AM
I agree with you Dingman, except many times the customer doesn't remember this (and sometimes neither do I - due to different min. HZ - sometimes 10, somtimes 15 etc.). Again, as I said it has more to do with how a person might be thinking.

Actually, I wish they would set it at 0 -60 and let me set the minimum through our software.

just_opinion
02-01-2007, 02:11 PM
Generally if my voltage is not doing anything below a certain point, I'll change my scale to match. ie:

2 volts = 20% = 12 HZ (just an example)

10 volts = 100% = 60 HZ.

I do it this way because I don't have to think about different translations.

This is not always possible at the controller level (adjusting the voltage range). It all depends how you think.

I do agree with.

But we must be careful on the VFD setting that 0 volt is equal to 20% (12 HZ). And not to ignore any signal from 2 volt down to 0.

Otherwire our PI will hunt more.

lwarren
02-01-2007, 03:34 PM
If a VFD guy told me to scale that way, I'd just tell him no. Unless you need that extra resolution for control purposes, then there is no reason for it and as you've mentioned, it causes more grief for you and the customer and anyone coming behind you to troubleshoot it.

Nope, 0 VDC (IMO) should always be 0 Hz (zero output from the device)
and
10 VDC should be 60 Hz (100% output from the device).

It just depends on where you want your control loop to start ramping. If the drive is set for 20hz min and your loop is set 0v-0hz then your not going to start ramping that drive until your loop gets to 3.3 volts.

If you wanted a tighter control loop then you would set your loop 0v = min
10v = max

PrestonPierce
02-01-2007, 05:32 PM
Ok, so it seems to be a split decision amongst control guys, I think I would keep doing the more staight forward approach where my 0 = 0hz and my 10 vdc = 60 hz, although I fully understand that I could possibly attain tighter control of the device if I used 0vdc=min and 10vdc =max hz, but as I said earlier it doesn't make that much difference on the systems I'm workikng on, the 0 to 60 just doesn't have a problem with control, I may adjust the throttling range or increase the filter on the staic sensor tip but over all I usually do not have to adjust anything , if I start with a .5" to1" throttle and a .1 Integral gain, no dervative.

svc
02-01-2007, 05:56 PM
I have always tried to use 4-20ma for two reasons. Tighter control and less issues with induction from high voltage. And 0hz=4 while 60hz=20 . All my applications have fallen within this range. I can see where pid could get confused when 20hz=0vdc if the drive is allowed off and on. Depending on the drive It could be a programming nightmare to tweak.

PrestonPierce
02-01-2007, 06:16 PM
Yeah 4 to 20 or 2 to 10v, they speced a 0 to 10 on this one so I had to throw a resistor on it, my outputs are all current, so I know what you mean its a scaling problem and unnecessary to do. On the same job I have two pumps that have a 12 hz minimum, so it gets unnecessarily confusing if I start scaling to someones minimum because there is no standard, if I stick to using my signal to represent 0 to 100% then I don't have to worry about what they set the minimum at, why do all the math, and make it confusing for the next guy and the maintemance men ?

svc
02-01-2007, 06:26 PM
amen brother I dont know how many times Ive programmed something that had specific requirements by the architect/engineer that caused much confusion. especially considering there are usually 3 or more involved in setting up controls. the control contractor ,the mechanical contractor, and the air balance company or companies. Everything has to mesh well.

codewriter
02-01-2007, 06:48 PM
I have never seen a vfd that will only accept 0-10vdc input, thats news to me.

anyways, I think you all are missing more than just the technically correct reason to scale properly.
If the VFD has its min hz set at 20, and its using a 0-10vdc input, you could be giving it 2vdc and the drive is still showing 20hz, or 2.5vdc and its still showing 20hz, you think thats not going to cause grief for the tech down the road?

If your having your VFD turn on and off frequently due to it going past setpoint even when running at 20hz, someone either sized something improperly, or it should have had 2 sources with 2 vfd's.

If your using the sleep function that is common in most vfd's, and you set it properly, you wont have that cycling problem.

Personally, I think using the VFD Enable input to enable the drive, which will set the vfd to 20hz (based on application), and then ramp up from there with a 4-20ma signal is the best way to go in most applications.

Why would anyone take what the graphics show into consideration? If you cant display things properly, you either need to give better training, or look at some new software, not dumb down a proper control sequence because it makes it easier for you to deal with.

Not trying to sound like an A@ here, but I remember many years in the field fixing things like this because the person whom designed/tuned the system wanted the quick and easy.

As oisys says, just my humble oppinion... (BUT IM RIGHT!) :) lol

PrestonPierce
02-01-2007, 07:06 PM
its not just about making the graphics display the right value, doing the math and showing it on the screen is not a problem, its about giving them the correct information, if I tell them that I am sending a 4 volt 40% signal they should expect to see a 40% signal on the screen. and a 40% readout on the display on the drive and would also expect that the drive is at 24 hz, how would you make all those match up ?

codewriter
02-01-2007, 07:23 PM
For my screens that display hz, for example on a AHU supply fan:

Command and Status
If off, then it reads 0hz, if on it reads 20-60hz, or what ever the true range is.

VFD Enable DI open = VFD off, 0hz
VFD Enable DI closed = VFD on, 20hz
4ma = 20hz
20ma = 60hz

I also do many where 0&#37; is min hz, and 100% is max hz. Most users are not going to climb around their building making sure the graphic and the vfd read the exact same percentage at any given second, plus since you seem to not be the one who is actually setting up the vfd param's, how do you know that the output freq will always be dead on the ref. freq? The vfd guy could have very well thought you a moron and built in a little protectoin of his own to protect his drive.

Now, if using a LON card, displaying the exact and true value is simple for anyone. Can't say I would recommend actually controlling it through the network, but feedback, status, alarms, temps, etc... its perfect for that. I try to keep unit logic built into a single controller and use hardwire i/o. Unless its not a critical application, but its rare I do anything that is not requested to be near bulletproof and will fall back to an acceptable working condition due to something happening to the network.

PrestonPierce
02-01-2007, 07:37 PM
Those setups are fine for us, I totally understand your point and I agree it is probably the best thing to do controlwise, but it is the customer that that I am trying to give the best and most accurate info to, these guys don't understand scaling, if I tell them its 40% it needs to be 40% every where they read it, if the drive guy did some extra protection on his own its on him, he was told to set the minimum in the drive it was speced to be there, granted if I had a lon card on it, it would make everything a lot simpler but over the whole job I would have to explain the drive setup to them and then explain a different pump setup to them, if I can just tell them that 50% is 50% it makes things a lot easier for everyone, the guy reading his PC screen is about 20 feet away from the display on the drive, if I couldn't make them match up I woud know about it fairly quickly,, I just don't see enough here to make me consider changing my method, it is straightforward and controls well.

codewriter
02-01-2007, 09:02 PM
I dont see how your even really making it match up. If 0vdc is 0hz to you, and 10vdc is 60hz to you, then your saying that 0&#37; control output is 0hz and 100% control output is 100hz, but since your obviously stopping at 60hz, your 100% output control signal will show 60hz on the VFD. Can you explain what you mean, I must be misunderstanding because the way I see it that method does not "work" either.

simsd
02-01-2007, 10:38 PM
We use Tridium AX as our intreface for graphics, so we can do anything we want. What we do is if there is anything unusual with the equipment, we will make notes right on the graphics screen (ie: Min. Fan speed = 10 Hz when enabled).

I understand your dilema about matching up in the 40% scenario and trying to be consistent throughout the setup process, but hey you're trying to match up different things from different manufacturers that all work in different ranges.

osiyo
02-02-2007, 06:56 AM
I was doing a start-up on a AHU, var speed discharge air control with a preheat coil and var speed exhaust. Anyway the unit/drive guy tells me while doing his start-up that I should scale my 0-10vdc signal output to coincide with his , 21hz (minimum) to 60hz ?,, result was that my 0-10 operated between 21 hz and 60 hz ? how do you guys do it,

To begin with I never allow the VFD guy to tell me how to set up my system or what the front end displays. Not his job, it's mine. And I'm the one who has to both make the entire system work and make it understandable to the customer.

That's if there is a VFD guy. Depends. On make, who bought it, etc. On some projects I am the VFD guy. As we bought em and I'm certfied to do the startups on some brands.

Anyway, I tend to favor setting up minimum speed within the VFD logic itself. And my screen displays will show 0-100%. It's easily explained to the customer. "Mr Customer, at zero signal from the system, Run Enabled, the unit will still be spinning in idle mode, a minimum speed."

I've yet to have a customer be confused by that.

Run Disabled and 0% on front end means unit is shut down. Run Enabled and 0% on front end means unit is idling and it's display will show 12 hertz (for example). Run Enabled and 50% on front end means VFD display will show 30 hertz. Run enabled and 100% in front end means VFD display will show 60 hertz. (Granting a 60 hertz maximum set up in the VFD)

And granting that we're displaying Hertz at the VFD. This varies, primarily according to customer preference. It's the most often chosen view by our customers. 2nd most chosen is a 0-100%. (In which case with Run Enabled and zero signal displayed on front end, they'd see 20% locally at the VFD) They almost never want amps or rpm except in a sidebar. Reasonable as most aren't gonna remember right off the top of their heads what the max allowable amps are for THAT particular motor, or max allowable RPM.

In any event, customers seem to have little trouble understanding that zero displayed at front end means the "puter" isn't trying to do anything, for whatever reason. But they'd expect to see 12 hertz (or 20%) on the VFD display. That's "idle". They understand that. And if front end says 50%, they can easily do a check of VFD panel and verify that it's showing 30 hertz or 50% at the same time. If it does, all is well, things match.

They seem to have absolutely no trouble with the "idle speed" concept. After all, if they drive a car they know the car motor idles at some minimum speed even if their foot is not on the accelerator. BUT ... if front display says 50%, meaning the "puter" is trying to achieve some controlled output power in order to do something, they wanna see 30 hertz or 50% in the VFD's display. Just as a little reassurance that everything is kosher.

But this is just my experience. Doesn't mean it's the only correct answer, as there is no such thing. Likewise, we do have the occassional customer who does want Amps as the primary number on the VFD display (the BIG number), and ohers who want RPM. And some who want everything to match up and down the scale between front end display and VFD's local panel. But they're the minority. Tend to be more technically savvy.

Tho sometimes they're not, they're just anal. I'm thinking of an in-house maintenance/controls guy who works for one of our larger customers. Geez, what a pain. Anal, with OCD (obsessive-compulsive disorder). Highly intelligent ... in the useless sort of way. He can read, and understands what he's reading ... but seems to have a complete inability to relate book knowledge to real world conditions. ie If he sees 50% signal from control system to supply fan VFD. He expects to see 50% on VFD local display, AND he expects fan should also be putting out 50% of it's rated CFM and that Amps should be at precisely 50% of rated max amps. If this is not true, my phone will ring off the hook. I've tried and tried to explain reality to him, that these things are NOT linear. But I might as well be talking to a wall.

Worse, once I get him to just take my word for it, the one issue, that it works, so go away. He doesn't actually learn. Of "get it". Next time I'll get a call from him about something like, "Okay, your front end says says OA damper on AHU#2 signal is 30%. But I did the math, using RA temp, OA temp, and MA temp. And the math says we're only getting 15% OA. There is something wrong and I want you to come fix it." I'll try to explain that, "Who cares, really?" That the real issue is that dampers aren't linear in operation, either. Between their design and the exact conformation of ducting, etc there is no one to one correlation between controller signal and the precise percentage of outside air. Nor does it matter. Controller is outputting whatever signal it needs to get required CFM of OA and/or achieve a desired MA temp. Period, end of subject. Depending on damper design and the ducts it might need a 25% signal to get that first 10% OA CFM. Then might only need 32% signal to double that to 20% OA CFM. Then only 36% to get 30% OA CFM, etc. At some midpoint, it might need BIG swings to get much change. It's NOT linear. And doesn't really matter. Are yah getting required OA CFM as calculated for the given moment? And/or is MAT at setpoint? They are? .... please go away and get a clue.

Sorry, my rant for the day. Actually I don't tell him to go away and get a clue. I'm patient with him, and will explain and re-explain many times. But it does get frustrating. Doesn't seem to ever sink in with him. It's as if he can't see the forest because all those trees get in the way of his view.

simsd
02-02-2007, 08:47 AM
osiyo,

I like the "highly intelligent..in the useless sort of way " part.

I hope hope you guys are charging him a ton of money.

leaflying
02-02-2007, 10:23 AM
My vote is 0-10v=0-60hz.

svc
02-02-2007, 11:43 AM
I am not familiar with your control scheme but cant you use the feedback signal from the drive to show true %. So that even at minimum drive speed you are using true reference not your input signal.

PrestonPierce
02-02-2007, 04:40 PM
I am not familiar with your control scheme but cant you use the feedback signal from the drive to show true %. So that even at minimum drive speed you are using true reference not your input signal.

"of course if I had a reliable feedback from the drive I wouldn't have to worry about it, but I don't."

was part of the first post,

they didn't spec it so we didn't use it. funny thing is that they did spec it on the pumps, I typically will not give them anything that isn't speced but I'll be more than happy to sell it to them later,
they also specified a non-adjustable reset for the discharge air :rolleyes: , I already have the change order for that one,,:) see if I just arbitrarily put it in there, and then they have problems they'll rip the control sequences apart trying to make it someone else's fault, but if I just grin and wait till the building overheats as it is doing right now, I'll get paid to change it, then I stick it to em, charge 8 hours to redo prints and 8 hours to make the change.

svc
02-02-2007, 08:52 PM
ah, confucios say man who stand on toilet get high on pot! I'm curious to what kind of drive and static controller you are using?

PrestonPierce
02-02-2007, 09:09 PM
Its a Yaskawa drive, the panel is a TAC product.

PrestonPierce
02-02-2007, 09:15 PM
sorry double post.

kittydog42
02-05-2007, 11:53 AM
I set up the drives 20Hz to 60Hz typically, but I send the speed signal as 0-100% and read back the speed signal as 0-100%. The drive ignores the speed signal until it reaches 33%. This way, I don't have to mess with the display, scaling or any of that. I almost always use modbus to control my drives so this is easy for me to do with any of the drives I typically use, which are ABB, Danfoss, and Square D.

dingman
02-05-2007, 12:33 PM
Well, you used alot of electrons to say it, but this is my reasoning also. That's exactly my POV.

I sympathize with you and your anal customer. Good luck.

To begin with I never allow the VFD guy to tell me how to set up my system or what the front end displays. Not his job, it's mine.
CLIP

Sorry, my rant for the day. Actually I don't tell him to go away and get a clue. I'm patient with him, and will explain and re-explain many times. But it does get frustrating. Doesn't seem to ever sink in with him. It's as if he can't see the forest because all those trees get in the way of his view.

PrestonPierce
02-05-2007, 05:43 PM
To begin with I never allow the VFD guy to tell me how to set up my system or what the front end displays. Not his job, it's mine. .

Sorry but that doesn't work here, even if it is your job if it doesn't meet every edtail in the spec, the only reward you will get for doing it your way is a chance to do it over,

osiyo
02-06-2007, 12:12 PM
Sorry but that doesn't work here, even if it is your job if it doesn't meet every edtail in the spec, the only reward you will get for doing it your way is a chance to do it over,

Of course, if it's in the details of the specs, and the customer can not be persuaded to allow a variance or change, you do it as the spec specifies.

Not what I said. I said I don't allow the -VFD- guy to dictate how I do things as far as front end presentation of data, or control sequences except as far as matters concerning the safe and reliable operation of the VFD is concerned. Etc.

I haven't a clue how things are done where you live and work. Around here, if a VFD rep is used to set up and commission the VFD itself. He comes in, does that, then he's gone. Considering his duties and responsibilities as having been completed.

OTOH, -I- or one of my peers or the company for whom I work are held responsible for proper overall operation of the entire system. IAW the specs, or IAW "Best Practices". VFD guy doesn't get the call back ... I do. VFD guy doesn't get the blame and maybe bad rep if the system doesn't work, or doesn't work as the customer wishes it to ... I do. VFD guy doesn't have to document and then train customer on system operation and troubleshooting from the front end ... I do. VFD guy doesn't have to change the graphics and/or control logic if such does not suit the customer ... I do.

I stand by what I asserted before.

There are a couple issues, IMHO.

First, VFD guy -PROBABLY- (but not always, depends on specific guy) knows more about his VFD than I do. I do listen to him, and consider any advice he gives very seriously. But almost certainly ... and in 100% of the cases I've dealt with personally (and that's a LOT of jobs) ... I know more about the overall system operation and it's requirements than he does.

Secondly, I'll have read those specs ... ALL of them, closely. After all, that is part of my job. And if I've any questions about anything within them, I'll have already discussed those and ironed out the details LONG before the VFD guy shows up. Typically, most of the time, around here the VFD guy looked at the specs, only the parts that he thought concerned him ... for about 5 or 10 minutes .... about an hour before he arrived to do his setup and commissioning. At best, he glanced at em the day before. I personally know all the reps (well, almost all) for the most popularly used VFDs (for HVAC service) in this area. All of them for ABB, Danfoss, and Yaskawa. Most for Reliance, etc. There isn't a one of em who isn't so busy that he's not running around like a chicken with it's head cut off. Scurrying from job to job as fast as he can get em done. Always behind, and always late. One of the reasons I got myself factory certified for a couple brands. Convenience. Guy is supposed to be on site at such and such a time. But I get a call, he's way behind and off somewhere else. No idea when he'll make it to my site. Can we reschedule for next week? But customer/general wants stuff running TODAY ... I give em an option. Let me do startup, programming, testing. Fax em the paperwork. Sometimes they agree, sometimes not. Depends on how busy, how demanding customer/general is, etc. In any event, while not regular, it's also not infrequent for them to give me the go-ahead. I do it and bill whomever. In any event, I'm gonna normally know those specs far better than the VFD guy.

Third, in 90% of the cases, I'm gonna KNOW the customer and/or customer's engineer/consultant ... who wrote the specs ... far better than the VFD guy. Most of our work is with previously existing customers. And most of this stuff has been ironed out between them and us long ago. I KNOW what they want. I make it my business to know what they want. They're the ones who sign the durned check.

In cases where I'm unsure, I ask the customer. MAYBE the customer's hired engineer/architect/mechanical contractor. Maybe. Depends. Depends on how cooperative they are and how prompt in providing answers. If I think they're waffling, stonewalling, just have a "don't give-sh*t" attitude, or whatever ... none of those being uncommon for me to see, I'll corner customer and put the matter on the table directly. Always, the customer's best interests and wants are my first priority. After all ... if I haven't mentioned this before ... it's the customer who's REALLY signing that check.

Fact is, it's not that uncommon for an engineering/architectural firm hired by the customer to draft up a sequence of operation, a bunch of detailed control specs, and a points list ... all without knowing just all that much about control systems themselves, or front ends, or even how the mechanical equipment REALLY operates in any detail.

Geez, I wouldn't even be able to recall all the times I've sat with an architect/engineer and explained to him or her that something he or she wrote into the specs was wrong or wouldn't work ... as is ..., was confusing to installers AND to the future operators, was overly complicated or needlessly redundant (ie one engineer had spec'd a pump system which had it's own controller, perfectly useable ... and expensive, but called for us to take over direct control of pumps with yet another controller. With no logical reason whatsoever. Turned out that while he'd read the specs on the pump system and their built in controls ... he'd not actually understood much about what those controls did and were capable of doing.), etc and so forth.

Most times, if yah explain it well, they'll readily agree to the suggested changes. But sometimes ... well, they're stubborn or just don't want to admit they were mistaken. Other times, just don't care. They're engaged in designing another project, don't want to be bothered with this one again.

Point being ... all those folks; the designer/engineer, the mechanical contractor, the general site electricians, the general contractor, and that VFD guy ... come, and go. All claim they did THEIR jobs right. And will all claim, if there is a problem, that's it's the fault of the Controls Contractor.

I'm the one that's gonna get the callback ... first. Every durned time. And repeatedly. Why? I'm the CONTROLS guy. Probably the only one in the group who actually knows how it all works together, as a system. Almost always still on site wrapping up details and still doing live testing after everyone else is gone. Also the one who'll be on site later to hold trainning to explain to customer how all this stuff works and what it does. I'm a familiar face, and the name the customer probably knows best of the lot.

Besides ... customer probably does NOT know exactly what is the source of any particular problem. Is it electrical? Mechanical? Design problem? Just a control sequence problem? Problem with info presentation on the screen? What? Who does he call? Take a guess.

Who does he first blame? Take a guess.

Likely ... most of the time ... customer didn't even know there was such a thing as a VFD guy.

<Shrug> I'm not saying you're wrong. Far from it. We just perhaps look at these things a bit differently from a slightly different perspective. Plus, certainly our experiences would somewhat differ based up the fact we probably work different geographical areas and deal with different customers. One adjusts one's way of doing business and getting things done based upon one's unique set of past experiences and knowledge, according to the area and the people one works with, and so forth. If your way works for you, heck, keep it up and ignore me.