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 40" Digital Manometer range 
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Joined: Fri Jan 08, 2010 3:35 pm
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I'm posting this in the open forum area so EVERYONE can see this note!

The 40" range on the DM is a "HARD RANGE" you can NOT run the DM over 40"! It will stop reading numbers around 36" as you reach it's max voltage range and saturate the sensor. You can not continue to try and read test pressure over 40" as damage to the sensor can result if it's done over and over!

I thought this was pretty clear when it states 40" max range. If you need to test over 40" you need to buy the 100" DM which will allow you to test over 40"

The PTS Plans Flowbench is rated for 36" max testing pressure! The 40" DM was designed to work with this flowbench. If you are unsure of what you need to use for your application PLEASE contact me first before you do damage to the sensors!

I will start putting a warning sticker on future DM orders stating this!

Again the PTS Style Flowbench is not rated for HIGH depressions per my design if you modifiy the design or use my parts on your own flowbench design you need to keep this warning in mind, I can not continue to replace DM's that have been used outside their design scope! I'm already working on the edge of my profit margins on my parts.

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Bruce

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Wed Jul 25, 2012 6:28 am
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Location: Grantsville, Utah 45 min west of Salt Lake City
Bruce,
While we are talking about over-ranging the DM, what about the automatic motor speed controller? Can it be over ranged also? Lets say I set it to test to 50", number one would it even go that high and if it did would it hurt it just like the DM?

John


Wed Jul 25, 2012 11:04 pm
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The DM's are like water gauges without water, if you buy a 40" water gauge you can't test higher than 40" otherwise you would spit water everywhere . . . same goes for the DM's except they don't have water they have a membrane that gets damaged.

They do not have a limit-less range and I'm not sure why people are thinking they do?

40" will get you 40", 100" gets you 100" and 16" gets you 16", now the ranges work out to be less due to how the sensor and circuit works with linearity based on 0-10V output to the DAQ card. When the sensor hits voltage saturation the readings in Flowsoft stop and go no further no matter how much higher you go. The readings stop but the sensor still "sees" the increase in pressure, it's just not showing in the software display but it's getting over pressure.

Rick and I have talked about this in the past when it happened the first time but it seems like it's a common problem and I'm not following why it's a problem? We are looking at making some changes to the software for a on-screen warning of some sorts to let the user know they are reaching sensor saturation.

This would go for anything that uses a pressure sensor so the motor control is also effected.

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Bruce

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Wed Jul 25, 2012 11:19 pm
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What I was wondering though, is can I hurt the motor controller? I was assuming it had a pressure sensor in it also. Just want to be cautious before I start pouring the the pressure to it. Thanks Bruce you answered my question. What is the limit in the motor controller?

Thanks
John


Wed Jul 25, 2012 11:24 pm
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The motor control is either a 40" or 100" should be marked on the label?

Same max pressure rules apply

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Bruce

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Thu Jul 26, 2012 4:47 am
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Thanks Bruce. I always apprciate dealing with you.

John


Thu Jul 26, 2012 2:38 pm
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Location: oxford ,england .
bruce ,could you direct me to the motor controller specs and price page ?

thanks
robert

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Thu Jul 26, 2012 3:22 pm
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ivanhoew wrote:
bruce ,could you direct me to the motor controller specs and price page ?

thanks
robert


That project does not have a page of info, it has been kind of a forum project that I have yet to make into full production. If someone asks about it after reading about it on the forum it's been discussed.

I should look at getting some info gathered together and put something up about it.

Basically it controls a solid state relay using a pressure sensor which is manually set to your first test pressure point, from there on, any change made to your test part ie opening/closing the valve will change your motor speed to set your depression back to your first test point. It actually is designed to operate on various types of controls SSR's, VFD etc.

I've only used it on SSR's so far.

Should be some info on the old forum about the project, I'll see if I can find a link or two.

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Thu Jul 26, 2012 4:32 pm
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Robert,
The automatic test pressure controller contains it's own independent differential pressure transducer and a closed loop analog PID control circuit.
It outputs either an 0-5v or 0-10 volt dc control voltage.
This dc control voltage commands any motor speed changes to hold test pressure constant.

Also required will be a completely separate mains phase control power module, (or a VFD) which enables the dc control voltage to control bulk mains power to the motors.
How much motor Hp or Amps can ultimately be controlled, is dependent only on the power module or VFD you decide to use, there is no upper limit.

Just remove the existing speed control potentiometer from your VFD, and wire in the automatic test pressure controller in it's place, and you will be set to go.

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Thu Jul 26, 2012 6:30 pm
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As to overpressure with the transducers.

The max USABLE pressure range is an electrical limit, the output pressure voltage can only rise up so far before it "hits the ceiling" and any further pressure increase beyond that will not drive the output voltage up any higher.
It very effectively sets the maximum pressure we can measure.

The max SAFE pressure is a very different thing.
These transducers are fairly tough, but not totally indestructible.
They can be driven considerably higher than the rated usable pressure range before they are stressed to the point of the characteristics permanently changing.
Rather like over stretching a steel tension coil spring, it won't come back to it's original length if you pull it out too far.

But like any precision measuring instrument, abuse is something to be carefully avoided.

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Last edited by Tony on Thu Jul 26, 2012 9:20 pm, edited 1 time in total.



Thu Jul 26, 2012 7:23 pm
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