[FUN] Digital I/O

[Stephen Mitschke]

Hi, I am looking for some feedback on Discrete positioners and low powerSolenoidsMy new plant has approximately forty plus Digital outputs for solenoidoperated valvesa) 8 solenoid operated valves with limit switches and which must fail inlast positionb) 8 Solenoid operated valves with limit switches and which fail to failsafepositionc) 24 Solenoid valves/dampers etc without limit switches and which fail tofailsafe positionFor (a) and (b) I'm contemplating Topworx Discrete positioners or Pepperl &Fuchs Valve coupler. Does any one have any feedback on these units or any alternative products.For (c) I plan to use Fisher Rosemount H1 Carrier with 8 Digital in and 8Digital out located in an Instrument Junction Box. There will be severaljunction boxes due to location of solenoids.My dilema with (C) is that we would normally use 24VDC solenoids 12 watteach, run via 1.5mm2 cable up to 150 MetresTo run 8 equivalent 24VDC solenoids via H1 Carrier plus Digital I/O over 150Metres (4 Amps@24VDC with max Volt Drop of 1.5Volts) I will need to run upto 16mm2 (10mm2 is too small) 2core + Earth cable to the IJB.This is a monster cable not to mention the termination strip.I am now looking at low power solenoids as an alternative.Does low power have any disadvantages (like loss of grunt)?Are they up to the job?.Has anyone got any comments or experience to share with low power solenoidsand Fieldbus equipment. I would appreciate some feedbackFinally : When control valves have been using 4-20mA to open and closevalves for the past few decades why have solenoid valves needed up to500mAmps to do the same job. RegardsAmbrose Hargan

[Stephen Mitschke]

Dear Mr. Hargan,a, b) Another alternative for on/off valve is the Automax-FlowserveBUSwitch. It is pneumatically actuated so the currents involved are small.c) Another alternative for remote discrete-I/O is the Smar DC302. Itconnects to H1 and has 16 DI and 8 DO so it is ideal for 8 valves with twolimit switches.Any chance you could run 110/240 VAC into the field and convert to 24 VDCcloser to the solenoids?Finally: control valves only need 4-20 mA because it only powers thepositioner. The actuation is done by pneumatics. For solenoid valves thecurrent does the actual actuation. I'm not a solenoid expert, but manysolenoids draw 30 mA and still provide some force. I have only heard doubtsabout the extreme low power ones, 1-2 mA.Jonas Berge (Smar)

[Stephen Mitschke]

Dear Ian,Dear Ambrose,sorry for putting myself as a potential supplier into the game but theGerman test-laboratory Infraserv (former Hoechst!!) is setting up atest-environment for FF projects for a number of companies. They will againtest the Pepperl+Fuchs FF valve control box together with low-powersolenoids because the background is zone 1 installation and Ex-iinstrumentation. Final results should be available around February.The Pepperl+Fuchs valve control box is not just a simple discrete I/O blockbut allows you to allocate a function block and by this implementingdecentralized control already on a valve / sensor level. For example thevalve box allows you to internally measure the time constant between openingthe solenoid and the feedback signal of the on/off sensing device. This is avery practical method to determine alterations, friction etc. in the valveas such. This you can do with FF only! Of course the valve box alsorecognizes cabel breakage or short circuit of either sensor inputs orsolenoid outputs.For the low-power solenoids there is quite a reasonable amount of experiencein Germany because they always struggeled with the Ex-i instrumentation ofas much different devices as possible. I will pass this e-mail also to thehead of the infraserv test laboratories, Mr. Manfred Dietz. Manfred Dietz isvery experienced senior measurement and control guy who defenitely can giveyou some background on the low-power solenoids and their reliability.Best regardsGuntherDr. Gunther KegelManaging Director Pepperl+Fuchs

[Stephen Mitschke]

I believe the Topworx valves would be ideal for what you want, as you haveindicated. Your application is similar to one I am currently awaitingapproval to instal, with failsafe fieldbus discrete valves.I believe the reason the current has been so high with discretes islaziness, and the fact that the inherent design of a control valve is "pilotoperated" already. There fore the solenoid only needs to move very smallamounts of air. It is not really difficult to adapt that concept, but itobviously costs more. The topworx valves have a very low current version.Russell Mackenzie Coogee Chemicals Australia

[Stephen Mitschke]

Ambrose,I am aware that the Festo company (www.festo.com) manufactures a range ofextremely low power solenoids (less than 1 watt @ 24 VDC) which can bearranged in a valve bank with common air supply and exhaust manifolds. Thereare quite a few possibilities about how these units can be arranged with on/ off, two and three way and multi-port options. Further, the design of theunits allow for bus technologies to drive them. I have had experience withthem using Profibus DP. I know they also support ASI bus and Interlink.Given the discrete nature of these valves, I'm not sure that FoundationFieldbus is your best option and you will only find one or two vendors whocan supply you with a FF registered discrete input and output modules.The method of valve control you have described is quite dated - this mightbe an opportunity for you to review your proposed design.HoneywellGreg BelcherAutomation and Control Solutions

[Stephen Mitschke]

I am presently the fieldbus engineering representative for ChevronTexaco.ThanksCan you also forward my comments to Ambrose Hargan.We do not recommend the use of low powered pilot assisted solenoid valvesdue to spurious trip related problems experienced at some of our operatingfacilities caused by mechanical shock. Even if the solenoids are mountedinside an enclosure on an independent mounting stand they can still beexposed to mechanical shock caused by mechanical work related activities inthe area. Before selecting low powered pilot assisted solenoid valves therecommendation is to do extensive testing while exposing the solenoids tothe mechanical shock levels that may be experienced at the installedlocation.Deon F. RaeStaff Instrumentation Engineer> ChevronTexaco, ERTC, Process Automation

[Stephen Mitschke]

At Woodside Energy we utilise hundreds of low power pilot operatedIntrinsically Safe solenoids on the majority of our offshore Shutdown andBlowdown valves. Deon's recommendation to undertake extensive testing is a very wise one. Wetested 9 valves and three met our criteria. As a result we have total confidence in our low power solenoids and have,to my knowledge, never had a Emergency Shutdown/Blowdown valve close owingto mechanical shock.Jim RussellPrincipal Instrument EngineerOffshore Technical ServicesWoodside Energy LtdPerth, Western Australia > -----Original Message-----> From: Verhappen, Ian [SMTP:verhappen.ian@syncrude.com]> Sent: Wednesday, December 12, 2001 2:53 AM> Subject: FUN] Digital I/O> > I am presently the fieldbus engineering representative for ChevronTexaco.> Thanks> > Can you also forward my comments to Ambrose Hargan.> > We do not recommend the use of low powered pilot assisted solenoid valves> due to spurious trip related problems experienced at some of our operating> facilities caused by mechanical shock. Even if the solenoids are mounted> inside an enclosure on an independent mounting stand they can still be> exposed to mechanical shock caused by mechanical work related activities> in> the area. Before selecting low powered pilot assisted solenoid valves the> recommendation is to do extensive testing while exposing the solenoids to> the mechanical shock levels that may be experienced at the installed> location.> > > Deon F. Rae> Staff Instrumentation Engineer> > ChevronTexaco, ERTC, Process Automation