Post by thread:[EE]: Flow sensing

Hi PIClisters, I need to check whether there is a water flow in a 1" rubber pipe. I thought about a so-called rotameter at first. It is made by Krohne. I got an offer for $840 which is hardly affordable for that project. Any alternative suggestions are welcome - I do not need the amount of the flow, only whether it is there or not. Thank you in advance. Imre -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

This is a somewhat self-serving plug, since I designed the electronics for it... I have a client that sells a product that would work for you, I think. http://smartflow-usa.com/switching_flowmeter.html The DDS-3B model would most likely be the model you'd want but it will depend of the flow rate you have in your system. Last I checked, they sell for about $250-$300 USD in single unit quantities. It used to have a PIC in it, but has an MSP430 in the the current models... ;-) Matt Pobursky Maximum Performance Systems On Thu, 19 Aug 2004 20:40:51 +0200, dr. Imre Bartfai wrote: {Quote hidden}> Hi PIClisters, > > I need to check whether there is a water flow in a 1" rubber pipe. I > thought about a so-called rotameter at first. It is made by Krohne. I > got an offer for $840 which is hardly affordable for that project. > Any alternative suggestions are welcome - I do not need the amount of > the flow, only whether it is there or not. > > Thank you in advance. > > Imre > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hi, On Thu, 19 Aug 2004, Matt Redmond wrote: > I have an uncle in the water systems equipment business. He asks these questions: > > Is the water being pumped? Yes and not so. The water is pumped from a kind of refrigerator to a laser gun (2kW nominal power) and delivers the heat from it to the refrigerating device. The real problem is that the laser gun may stop the flow if shuts down. I need to detect this stop and cancel the pump. The test of the inflow pressure seems not to be appropriate as the pump has some integrated electronics which regulates the pressure accordingly so - as the customer told me - there is only a little pressure increase, if any. There is a huge amount of pressure drop between the inflow and outflow side (the gun has a significant resistance). An idea would be to check the differential pressure but it seems me a bit complicated (I would need to tap both pipes which should be avoided). > How small a flow are you trying to detect? (in gal/min)? Approximately 2000 l/h. > Horizontal or vertical flow? As you want because of rubber pipe. > > With that he can probably tell me to tell you where to look for an appropriate device. > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hi, this seems to be promising. Only the bureacracy can disturb the nice impression (transport+fees, customs, &c.). I store this as a 2nd best resort for the case. Thank you for the information. If I could persuade them to use DHL for transport... (U*S is a plague...) Imre On Thu, 19 Aug 2004, Matt Pobursky wrote: {Quote hidden}> This is a somewhat self-serving plug, since I designed the electronics > for it... > > I have a client that sells a product that would work for you, I think. > > http://smartflow-usa.com/switching_flowmeter.html > > The DDS-3B model would most likely be the model you'd want but it will > depend of the flow rate you have in your system. Last I checked, they > sell for about $250-$300 USD in single unit quantities. > > It used to have a PIC in it, but has an MSP430 in the the current > models... ;-) > > Matt Pobursky > Maximum Performance Systems > > On Thu, 19 Aug 2004 20:40:51 +0200, dr. Imre Bartfai wrote: > > Hi PIClisters, > > > > I need to check whether there is a water flow in a 1" rubber pipe. I > > thought about a so-called rotameter at first. It is made by Krohne. I > > got an offer for $840 which is hardly affordable for that project. > > Any alternative suggestions are welcome - I do not need the amount of > > the flow, only whether it is there or not. > > > > Thank you in advance. > > > > Imre > > > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> I need to check whether there is a water flow in a 1" rubber pipe. Are you looking to make something as a one of ? If so, how about a centrifugal pump of about the same capacity, pull out the motor magnets and replace with a simple opto device. That way you get an impellor in a sealed housing that is designed to have the right sized hoses. You'd find those types of pumps in boat bilges, ponds, washing machines, etc for a lot less than $840. Steve. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Hmm. Still need to know what flow is. My uncle mentioned this flow switch: http://www.pottersignal.com/industrial/products/flowandpressure/pdf/IFS.pdf which requires 4.5 gal/min of flow to trip. Another possibility is a pressure transducer like this: http://www.omega.com/pptst/PX40.html - the 0-15psi model might work for you. You said little if any pressure in the line - but that's not possible if you are getting flow (like current without voltage). -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

If you can afford a DIY solution then make a section of the hose translucent, affix a cage with a ball in the hose, and put the assembly vertical - use an optosensor to see if the ball is up during flow, down when no flow. Make sure the ball is about the same specific gravity as the solution so it doesn't float naturally, or sink even during flow. Can also use impeller blades, or other objects. -Adam dr. Imre Bartfai wrote: {Quote hidden}>Hi PIClisters, > >I need to check whether there is a water flow in a 1" rubber pipe. I >thought about a so-called rotameter at first. It is made by Krohne. I got >an offer for $840 which is hardly affordable for that project. Any >alternative suggestions are welcome - I do not need the amount of the >flow, only whether it is there or not. > >Thank you in advance. > >Imre > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

www.dwyer-inst.com -----Original Message----- ... I thought about a so-called rotameter ... --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.740 / Virus Database: 494 - Release Date: 16/8/2547 ________ Information from NOD32 ________ This message was checked by NOD32 Antivirus System for Linux Mail Server. http://www.nod32th.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Try an ultrasonic flow meter. Basically you aim a 40 KHz tx/rx at the pipe and if there is a phase shift, you have flow. It gets a lot more fancy if you want to know the exact flow, but for your application it should work well. For more information, google ultrasonic flow meter. I love the idea since it's non-invasive. This was the reason why I was searching for ultrasonic pairs about a week ago. :) Hope this helps, Aaron Tufgar -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

You know, an alternative to that would be to use the refraction properties of water to his advantage. Water does bend light. Shawn Wilton Junior in CpE MicroBiologist http://black9.net M. Adam Davis wrote: {Quote hidden}> If you can afford a DIY solution then make a section of the hose > translucent, affix a cage with a ball in the hose, and put the assembly > vertical - use an optosensor to see if the ball is up during flow, down > when no flow. Make sure the ball is about the same specific gravity as > the solution so it doesn't float naturally, or sink even during flow. > > Can also use impeller blades, or other objects. > > -Adam > > dr. Imre Bartfai wrote: > >> Hi PIClisters, >> >> I need to check whether there is a water flow in a 1" rubber pipe. I >> thought about a so-called rotameter at first. It is made by Krohne. I got >> an offer for $840 which is hardly affordable for that project. Any >> alternative suggestions are welcome - I do not need the amount of the >> flow, only whether it is there or not. >> >> Thank you in advance. >> >> Imre >> >> -- >> http://www.piclist.com hint: PICList Posts must start with ONE topic: >> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads >> >> >> >> >> > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>If you can afford a DIY solution then make a section >of the hose translucent, affix a cage with a ball in >the hose, and put the assembly vertical - use an >optosensor to see if the ball is up during flow, down >when no flow. Make sure the ball is about the same >specific gravity as the solution so it doesn't float >naturally, or sink even during flow. You can get flow-meters that work exactly this way. They are a conical clear plastic with an opaque ball in them. The ball is pushed up towards the wide end of the conical shape by the liquid flow. All you would need to do is mount an opto sensor outside it at a suitable height for the flow rate you have. You could probably put two sensors so that both are blocked at the correct flow rate, but you then have "low", "correct", and "high" indications for very little extra expense. You may need to enclose the whole thing in a box to stop extraneous external light from upsetting the sensing. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Of course. But it is a resin-filled black box... Imre On Fri, 20 Aug 2004, Russell McMahon wrote: {Quote hidden}> > ... the pump has some > > integrated electronics which regulates the pressure accordingly so - as > > the customer told me - there is only a little pressure increase, if any. > > If you can access these electronics they may well provide a signal that > tells you what you ant to know. > > > RM > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Sorry, it is not the case as it is a closed system like human blood circulation system. I thought all the suggestions, by the way. I will carefully investigate all the options, and thank you and all PIClisters for the valuable contribution. An important point is: a bad decision may be catastrophic as I would falsely detect a stop of the flow and therefore the logic halts the pump but in the reality the flow is not stopped (and the laser gun runs). It would blow up. Of course, the customer's request was to stop the pump if the flow really stopped because of it shortens the life span of the pump. Regards, Imre On Thu, 19 Aug 2004, Ken Pergola wrote: {Quote hidden}> dr. Imre Bartfai wrote: > > > I need to check whether there is a water flow in a 1" rubber pipe. > > Hi Imre, > > Are you able to use or have access to a section of pipe that has no water in > it when water is not flowing? > If so, I'm wondering if a Motorola/Freescale E-field sensor might be able to > be used in your application. > > Best regards, > > Ken Pergola > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

dr. Imre Bartfai wrote: > An important point is: a bad decision may be > catastrophic as > I would falsely detect a stop of the flow and therefore the logic > halts > the pump but in the reality the flow is not stopped (and the laser gun > runs). It sounds like that is more important to address. If the flow stops - for whatever reason - the lazer should be turned off quickly. Or perhaps a thermal sensor on the lazer shuts it off before damage occurs. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Ok, can I ask you something? If, you make a small hole to the pipe and put a pressure sensor, it must work. There are sensors with precision down to 10 Pa, (that I used, there must be lower). 10 Pa is close to a blow if I recall that sensor would detect a blow directed to its input from a distance of 2 meters.... So, I must detect the pressure increasing when the flow is stopped but the pump still runs. When you detect the flow increasing, you shutdown the pump. And the "high" pressure will remain stable (you might need a non return valve after the pump) until the flow is allowed again by the laser... Now, why this wouldn't work? (just wondering...) :) Mauricio Jancic -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

{Quote hidden}>-----Original Message----- >From: pic microcontroller discussion list >[spam_OUTPICLISTTakeThisOuTMITVMA.MIT.EDU] On Behalf Of Mauricio Jancic >Sent: 20 August 2004 13:41 >To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU >Subject: Re: [EE]: Flow sensing > > >Ok, can I ask you something? If, you make a small hole to the >pipe and put a pressure sensor, it must work. There are >sensors with precision down to 10 Pa, (that I used, there must >be lower). 10 Pa is close to a blow if I recall that sensor >would detect a blow directed to its input from a distance of 2 >meters.... So, I must detect the pressure increasing when the >flow is stopped but the pump still runs. > > When you detect the flow increasing, you shutdown the >pump. And the "high" pressure will remain stable (you might >need a non return valve after the pump) until the flow is >allowed again by the laser... > > Now, why this wouldn't work? (just wondering...) :) A better way is to use two pressure sensors, one either side of a fixed restriction in the pipe. You can now measure the difference between the two sensors to get pressure drop (and hence flow) without having to worry about what the static pressure is (which may vary). Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. ======================================================================= -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

How about a simple pool / hot tub style flow switch, able to read at > 1 gpm, in the return line of the hose. Since you said that the concern was that the laser could interrupt the flow, then by monitoring the line coming out of the laser back to the pump, you could tell quite easily whether the laser has closed it's valve or not. These flow switches are usually in the area of $50. Google for water flow switches, or go down to the local pool dealership. --Joe Jansen -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> Sorry, it is not the case as it is a closed system like human blood > circulation system. a) the heat transfer method also works applied to the outside of the pipe (no holes) as long as the pipe is thin and an insulator (thermal) b) why do you not tap into the power supply of the laser (at the power cord) to sense the mains current ? I'd bet a large virtual sum there is a huge difference between running/not running. After all the power that could 'blow up' the tube comes from the mains, so, no power, no blow up, yes power, run the pump and cross your fingers. Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> Ok, can I ask you something? If, you make a small hole to the pipe and put a > pressure sensor, it must work. There are sensors with precision down to 10 > Pa, (that I used, there must be lower). ... > Now, why this wouldn't work? (just wondering...) :) If the pump has a pressure regulator, that effect may be within the noise. The pressure is probably not a nice steady signal where a minimal pressure change would be significant. Gerhard -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> b) why do you not tap into the power supply of the laser (at the power > cord) to sense the mains current ? I'd bet a large virtual sum there is a > huge difference between running/not running. After all the power that > could 'blow up' the tube comes from the mains, so, no power, no blow up, > yes power, run the pump and cross your fingers. Or, similarly to what someone else suggested (tapping into the pump's pressure controller), maybe you can tap the signal in the laser controller that controls the water flow? ge -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

You are right. That's why I plan the supervising circuitry (actually a Parallax BS2SX based box) gives an alarm which should be confirmed manually. There was also a suggestion of the customer to obtain the signal from the valve which is located in the laser gun housing and is controlled electrically. But I dislike this one as there is a lot of HV (20kV+) and if something nasty happens, then it may lead to endless discussion (at the court, maybe). So the strategy: if flow stops, then stop pump give an alarm until confirmed There is an option also to re-start pump forcibly in this case. On the other hand, if the whole system boots, there is no flow at the beginning, and it is NOT the signal to stop the pump. I guess an initial delay would help. Or the inflow pressure may also be monitored (beneath output flow) and the dp/dt could be also monitored. Imre +-----------------------------------------------------------------------+ | The information transmitted is intended only for the person or entity | | to which it is addressed and may contain confidential and/or | | privileged material. Any review, retransmission, dissemination or | | other use of, or taking of any action in reliance upon, this | | information by persons or entities other than the intended recipient | | is prohibited. If you received this in error, please contact the | | sender and delete the material from any computer. | +-----------------------------------------------------------------------+ On Fri, 20 Aug 2004, Olin Lathrop wrote: {Quote hidden}> dr. Imre Bartfai wrote: > > An important point is: a bad decision may be > > catastrophic as > > I would falsely detect a stop of the flow and therefore the logic > > halts > > the pump but in the reality the flow is not stopped (and the laser gun > > runs). > > It sounds like that is more important to address. If the flow stops - for > whatever reason - the lazer should be turned off quickly. Or perhaps a > thermal sensor on the lazer shuts it off before damage occurs. > > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Hi, I consider this option. However, the pressure must be looked at the forward pipe, and I wanted to check the flow in the return pipe. The problem is (as I mentioned before) the pump has a built-in pressure regulation with unknown characteristics, and I do not know whether and how the pressure varies under normal conditions. I am pretty sure it happens otherwise the pressure regulator would be superfluous. Imre On Fri, 20 Aug 2004, Mauricio Jancic wrote: {Quote hidden}> Ok, can I ask you something? If, you make a small hole to the pipe and put a > pressure sensor, it must work. There are sensors with precision down to 10 > Pa, (that I used, there must be lower). 10 Pa is close to a blow if I recall > that sensor would detect a blow directed to its input from a distance of 2 > meters.... So, I must detect the pressure increasing when the flow is > stopped but the pump still runs. > > When you detect the flow increasing, you shutdown the pump. And the > "high" pressure will remain stable (you might need a non return valve after > the pump) until the flow is allowed again by the laser... > > Now, why this wouldn't work? (just wondering...) :) > > > Mauricio Jancic > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.