Testament Posted January 14, 2015 Share Posted January 14, 2015 You can definitely get 300mm long lvdt linear positioners with 4-20ma output. It seems like the easiest and cheapest solution? Just need the additional I/o means of mounting and someone who can do the dcs/plc programming. The question is does the existing actuator and flap arrangement have a suitable characteristic and flow area and speed to provide stable control within the required parameters? Quote Link to comment Share on other sites More sharing options...
fletch Posted January 14, 2015 Share Posted January 14, 2015 you can get a positioner with 4-20 input that can have a remote feedback. That way you dont need any programming changes to your control system. Samson make one that i have used, also i think there is a new fisher one. pretty expensive, but maybe around $4-6k per unit incl a positioner is not bad if its self contained Or you could just slap in a small controller to run off your 4-20 and have it drive an i/p with an lvdt feedback Or, a rotary positioner with one of those stupid arms on it and a rod to the end of the ram. then you have everything built into one package. some of the big valves in one of the LPG plants i maintain have this setup. ill try and find a pic Quote Link to comment Share on other sites More sharing options...
sentra Posted January 14, 2015 Share Posted January 14, 2015 are you talking about a duct box with a bunch of slats that turn through 90deg that are supported by pillow blocks at each end? if you were going to end up running wires what would be your reason for not replacing the levers with sprockets and run a servo motor directly? Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 Those electric linear actuators are shit for what you want to do. option 2: http://www.omega.com/pptst/LD630.html I have used these before. they are mint. Look up LVDT positioner.many different types, probably can find cheaper and with a nz distributor with local stock. Nice smooth analog signal, easiest to work with compared to digital encoders -linear or rotary -also that link above is suitable 5-300mm so should be good. option 3: why not vsd? for 300kw motors will be spendy, but suprising the amount of energy you will save. i can get you a price if your interested, we get a good rate on them. why do you need new cables? Man that knows about electrical said the cables will be under rated for VSD's plus two of the fans run at 100% open on the dampers for 18 hrs a day, that and the fact the fans are ~800kg's each and small RPM adjustments will take ages and it will introduce hunt into the system. (have seen a converted VSD system which was pretty rubbish and had a large apetite for belts) Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 You can definitely get 300mm long lvdt linear positioners with 4-20ma output. It seems like the easiest and cheapest solution? Just need the additional I/o means of mounting and someone who can do the dcs/plc programming. The question is does the existing actuator and flap arrangement have a suitable characteristic and flow area and speed to provide stable control within the required parameters? Yip it's about a 8 foot circular duct with 20 vanes in it with a rotating linkage which moves each vane, seems to control OK when the actuators are moving steadily from rest, if they surge out too far it will trip the system, -ve safety is -80mm wg, so around .1 of a PSI. PLC programming won't be a drama once we get the parameters right.. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 are you talking about a duct box with a bunch of slats that turn through 90deg that are supported by pillow blocks at each end? if you were going to end up running wires what would be your reason for not replacing the levers with sprockets and run a servo motor directly? Pretty well as you describe (shuld have some pictures somewhere) I would need 64 of them across 3 fans which may get a bit untidy. and incorrect deflection of one vane at low open percentage could be a bastard to identify but would cause a pressure trip. Looking at the link provided by fletch and covered by tomstament that LVDT looks exactly like the sort of thing i need and is going to be pretty cost effective I will dig further in to this just need to convince one electrician whom is allergic to pneumatic and my instrument tech that is on the same wavelength as you guys about the electrical actuators / not going to please everyone.. Cheers for the feedback (heh) guys 1 Quote Link to comment Share on other sites More sharing options...
peteretep Posted January 14, 2015 Share Posted January 14, 2015 I dont think vsd's would be right for this I think you should do what I said with pneumatics and valving. pneumatics are simple and reliable Quote Link to comment Share on other sites More sharing options...
peteretep Posted January 14, 2015 Share Posted January 14, 2015 Is there a relationship between 'size' of cam and minimum idle speed? I am only part way through tuning my car but I have warm idle at just under 1000rpm which is pretty low I think, but as it is now, when I touch the throttle the engine stumbles, goes lean and takes a while to get out of the hole (relatively). How can I tune to stop this happening or should I just increase the idle speed a bit as I am fighting a losing battle? Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 You could consider the approach of "more air" and less timing which will give you the same idle rpm but should produce a torquier idle if you have a decent sized camshaft.. sometimes it just takes a bit of tinkeriing..add a bit of throttle open and dial back the timing to see how it behaves. You can also richen the idle and add timing which can help with torque (to a degree) My 1G starlet on standard cams actually performs better the other way around with less air and more timing to achieve a rock solid idle which it will climb straight out of. (used to have a stumble on blipping the throttle until fully warmed up, and would occasionally stumble / dip below idle rpm on return to idle..) what fuelling and ignition setup do you have? Quote Link to comment Share on other sites More sharing options...
peteretep Posted January 14, 2015 Share Posted January 14, 2015 its megasquirt with hall effect and ls2 coils, and jetski throttle bodies I will try backing off the timing and opening throttle plates a bit Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 Sweet, you should have enough adjustability to get it idling strong. Quote Link to comment Share on other sites More sharing options...
h4nd Posted January 14, 2015 Share Posted January 14, 2015 Man that knows about electrical said the cables will be under rated for VSD's plus two of the fans run at 100% open on the dampers for 18 hrs a day, that and the fact the fans are ~800kg's each and small RPM adjustments will take ages and it will introduce hunt into the system. (have seen a converted VSD system which was pretty rubbish and had a large apetite for belts) Yeah, Softstarters / VSDs are great in some systems, but the response time you mention makes the vanes sound good. OR tune the control loop frequency (latency). PID might do it. Cables he's talking about prolly refers to shielding. Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 Yeah, Softstarters / VSDs are great in some systems, but the response time you mention makes the vanes sound good. OR tune the control loop frequency (latency). PID might do it. Cables he's talking about prolly refers to shielding. Yeah that rings a bell about shielding / i'm no sparky. So i am still up for a means of controlling the ram, the current spring diaphragm method does work (when it's working) Quote Link to comment Share on other sites More sharing options...
peteretep Posted January 14, 2015 Share Posted January 14, 2015 single 5/3 spring centre, mid position closed and use plc to control based on time and pressure. Its hard to know exactly what you can do without knowing how rugged this stuff is, whether it can be electrically controlled or you want it mechanically controlled in case of electrical failure etc etc.is there back up pressure relief valves in case sensors fail Also the stuff you are working with is pretty massive and 20k isnt a huge amount of money to play with Quote Link to comment Share on other sites More sharing options...
Testament Posted January 14, 2015 Share Posted January 14, 2015 regardless of staying with the existing actuators or changing you DEFINITELY want actual position feedback on something that appears to be a critical control function requiring fine control. You can also use it to diagnose actuator sticktion and things like that if you are clever and make use of that for reliability/maintenance planning. e.g. figuring out its stuff is flogged out and overly loose or overly tight etc. Quote Link to comment Share on other sites More sharing options...
peteretep Posted January 14, 2015 Share Posted January 14, 2015 yeah but there are varying factors which control the pressure, so one location one day means something different the next day/minute. I realise having feedback to see what the dampers are doing is a good idea but their location seems to have pretty little relevance to operation Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 yeah positional feedback is a nice to have" for example have they returned to the "start position" prior to start. because bad things will happen if they are not, but as far as control goes you don't need the feedback. In all reality the current system does work but as soon as someone tinkers with the system and new rams are put on then it all goes out the window. this can happen when a operator decides to mess with some manual valves or start up another fan he shouldn't have... Hey i reckon the way the wind is blowing at the building has an affect too as the main inlet fan is positioned up against the west wall with a couple of layers of filters in between. plus the pressure inside of the building pays a part so even buildiong ventialtion fan filter condition will affect optimun start parameters. Here is a snap of the inlet damper on the hoist after it's birthday last year.. Quote Link to comment Share on other sites More sharing options...
peteretep Posted January 14, 2015 Share Posted January 14, 2015 seems to me like some better control and operator training would go a long way to making a better system tbh. what is all this stuff for? a 5 story high pressure vessel sounds pretty cray cray Quote Link to comment Share on other sites More sharing options...
mjrstar Posted January 14, 2015 Share Posted January 14, 2015 I agree on both counts... always blame the hardware though not the meat sitting on the chair in the control room... it's a powder drier (yip liquid flow in and heat affect the pressure control too) in operation the damper looks a lot like this - expect has a linear rather than rotary driven actuation. http://grabcad.com/library/o1300-vortex-damper Quote Link to comment Share on other sites More sharing options...
Testament Posted January 14, 2015 Share Posted January 14, 2015 yeah but there are varying factors which control the pressure, so one location one day means something different the next day/minute. I realise having feedback to see what the dampers are doing is a good idea but their location seems to have pretty little relevance to operation theoretically yes. but when you are trying to tune it or diagnose an issue its golden. e.g. is it operating an an almost fully open position or almost full closed, what is the actual rate of change of opening and closing vs where the controller is asking it to go. so yes you can operate/tune with just the process variable but its like driving with tunnel vision/ you have no idea you only just missed that logging truck by millimeters on that occasion. not sure what the failure modes of the system are or safety concerns but if its an inlet or outlet fan but in a upset or trip condition you probably would like to know things are fully open or shut too and have some kind of interlock on startup too maybe. Quote Link to comment Share on other sites More sharing options...
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