LandyManLuke Posted May 19, 2006 Share Posted May 19, 2006 Does anyone know where I could find a 1/4" BSP threaded pressure transducer, either active or passive, that doesn't cost ~£100. I was thinking about a project but it'll be floored if i need to spend anything near that much. Ta Luke Quote Link to comment Share on other sites More sharing options...
isuzurover Posted May 19, 2006 Share Posted May 19, 2006 RS components/electronics sell absolute and differential pressure transducers, starting at about €20 (10-15quid?). As well as honeywell for not much more. They are no threaded though - they are plastic with tubes to connect to wherever you need to. You need to make the rest of the circuitry yourself, but it is not hard. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 19, 2006 Author Share Posted May 19, 2006 Ta, I'll look, yup some plumbing isn't a problem. Luke Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 19, 2006 Author Share Posted May 19, 2006 K, there's loads! either need to find one 0 - 120 PSI 0 - 5 vDC ish, or crack some brain cells together for a driver/amp circuit. fun. Luke Quote Link to comment Share on other sites More sharing options...
galooph Posted May 19, 2006 Share Posted May 19, 2006 Have a look at Freescale - formerly Motorola. They offer free samples too if you're only after a handful. Dan Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 19, 2006 Author Share Posted May 19, 2006 Thanks for the link but they don't appear to go to a high enough pressure for what i'm after. Ta Quote Link to comment Share on other sites More sharing options...
simonr Posted May 19, 2006 Share Posted May 19, 2006 The ones I used on the air suspension 0-200psi, 1/4BSP thread are normally used in Air Conditioning. The ones with a voltage output are at least double the cost of the current output type (don't know why). Can't remember the exact spec, but it will allow a variable current to flow through the device. I just put it in a voltage divider with a resistor to +ve so the voltage at the junction of the resistor and the sensor varied proportionally to the pressure. Any of the 'Climate Centre' shops should be able to help. They still cost me £200 for 4 though. The other option is to use oil pressure sensors for cars. Several I found would read up to 150psi. They are pretty cheap, but I found the accuracy and tolerance lacking a bit. Si Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 19, 2006 Author Share Posted May 19, 2006 Have found 235-5908 on RS, seems ok, it's not quite linear, and'll need an amplifier, but then it's only a tenner, the next cheapest is 40 quid. might be worth playing with for such a saving. Si, i seem to remember you posting a link to solenoid air valves, still got the link? Luke Quote Link to comment Share on other sites More sharing options...
simonr Posted May 19, 2006 Share Posted May 19, 2006 Have found 235-5908 on RS, seems ok, it's not quite linear, and'll need an amplifier, but then it's only a tenner, the next cheapest is 40 quid.might be worth playing with for such a saving. Si, i seem to remember you posting a link to solenoid air valves, still got the link? Luke I bought them from Air Technics in Tonbridge (they are on the web). Si P.S - What are you up to??? Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 19, 2006 Author Share Posted May 19, 2006 It's a slightly..Ahem.... ...pointless project. comes from being a control engineering student, having a compressor in the workshop, and a spare PC/USB interface board. Tank pressure, regulator pressure, and a servo driving the regulator. simple control system here we come. monitoring duty cycle, estimating CFM and total air usage, other bits and bobs. Pointless really, apart from the fun of it, which is why i dont want to spend loads. BTW, if anyone's got a cheapie Machinemart compressor, take the crappy screw valve and reg off, the screw valve only has about 2mm bore any thoughts? - have you seen this before? Luke PS this has nothing to do with revision avoidance, what so ever.... Quote Link to comment Share on other sites More sharing options...
rtbarton Posted May 19, 2006 Share Posted May 19, 2006 I was considering a similar project, but was put off by the pressure sensor cost. I take it you were going to use the Maplin USB control board? I am using a battery of fridge compressors and propane bottles, the idea being to charge the bottles on off-peak electricity and have the compressors inside the building to recover the heat. I use a lot of compressed air, and the plan was to use software to switch the compressors, taking into account the nature of the job on hand so that unneccesarlily high pressure (ie cost) was not generated, using the minimum number of compressors to supply the CFM. Also the software could calibrate the compressors and every few days run a test routine, fridge compressors use oil and the take longer to raise pressure on low oil. The software would decide which compressors to use so that wear & tear was evened out, or if heat was required in a particular room the compressor(s) in that room would be used. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 19, 2006 Author Share Posted May 19, 2006 Yup, the velleman one. The last one, which used the parallel port, i built. i've decided the USB one is worth the price, and more useful!! These sensors look like they can get round the price issue, perhaps we should compare notes... Luke Quote Link to comment Share on other sites More sharing options...
simonr Posted May 19, 2006 Share Posted May 19, 2006 Mostly I've used these: Basic Atom for embedded control. Much easier than trying to interface a PC - and they have four analogue inputs. They are pretty good as an intelegent IO port for a PC too via the built in RS232. I reckon that they are as fast as most PC's driving the parallel port via VB - as it has none of the windows or VB overheads. The processor can be interrupt driven and there are timer based interrupts as well. It supports decent floating point, flash memory, a reasonable amount of ram and are programable in BASIC via a nice PC based IDE. Best of all, they are pretty bullet proof and use almost no power. I use two in the suspension controller 'networked' via the I2C bus. One drives the LCD display and reads the pushbuttons and the other is responsible for calculating the demand pressures and reading the pressure transducers & gyros + reacting to user input. I've used these and Basic Stamp processors for all kinds of embedded control applications. Si Quote Link to comment Share on other sites More sharing options...
rtbarton Posted May 20, 2006 Share Posted May 20, 2006 I've used the 8052AH-Basic in days of yore. I really wanted a parallel port interface so I could use an MSDOS based system with QBASIC-7, my aged brain won't cope with Visual Basic any more In the end I've decided that it would take too much time to develop an intelligent system, so I'm buliding a more conventional system, using two pressure switches, one set to 150 psi for overnight charging and one set to 100 psi for daytime use. Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 20, 2006 Author Share Posted May 20, 2006 Si, they're nice, and i found out how cumbersome the VB overheads are with the ITX project. We used 8051s last year, and atmega 16L this year, and one of my house mates has got some PICAXE stuff. Just need some spare cash for that atom board and devloping kit, it looks very nice. Have you got any info on your air suspension project, sounds interesting. Luke Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted May 20, 2006 Share Posted May 20, 2006 If you are any good with linux...try one of these: www.gumstix.org Have a look at the waysmall computers...and the price. PICs are dead easy...but its hard to make them do anything complex. Tried implementing a PID controller on one last year...failed miserably (but mostly due to servo phase lag and bad sensors....) Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted May 20, 2006 Author Share Posted May 20, 2006 grrr, i'm having enough fun at the mo trying to design a discrete compensator in matlab/simulink, and thats only a simulation. Just finished a modified PID for filling twin water tanks, very boring but some interesting integral windup solutions. suppose this is 110% OT now..... Quote Link to comment Share on other sites More sharing options...
TheRecklessEngineer Posted May 20, 2006 Share Posted May 20, 2006 Oh I dunno...could be applied to cruise control...or perhaps electric radiator fan speed. :S Quote Link to comment Share on other sites More sharing options...
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