RSI incorporated is introducing a new pressure measurement device. The device converts a strain gage measurement into a signal your PC can read, and the device ships with software that gives you pressure curves, statistical analysis, and a bunch of other stuff. RSI's strain gages attach without having to sand away the bluing. The devices are expected to ship in June, and RSI is taking orders now.

The RSI system (like the familiar Oehler 43) measures pressures for factory and wildcat calibers and requires no calibration with factory or proof ammo.

The PressureTrace system costs $189, and with the introductory offer, you get everything you need for three firearms.

http://www.shootingsoftware.com/pressure.htm

The Oehler 43 system costs $800, again with everything you need for three firearms.

www.oehler-research.com/model43.html

I've got me an RSI system reserved.

H. C.

(edit: I had spelled PressureTrace as "PressureTcace")

[ 04-26-2003, 19:39: Message edited by: HenryC470 ]

Actually, somebody called Southwest Products makes the PressureTrace, and RSI sells it. Southwest has a download page for a demo version of their software. My internet connection is having a bad hair day, and it's telling me I can take a 17 minute nap.

H. C.

http://www.swproducts.biz/default.htm

Hooeey!! Now we can all get pressure readings, just like the big boys!! Hmmm. Wonder how many of my 'perfectly safe' loads will cause heart palpitations once I see a pressure reading

R-WEST

Looks interesting. I might have to get one to compare with the M43 I use. I know my dad would love to have his own. Kind of steep for the strain gages though, the Oehlers are only $35 for 5 gages. You save enough money to make it worth it though. I wonder if the gages are interchangable between the Oehler and it. Hope it don't fade off into existance though, new products... ya just never know. Get em while they're cheap!

Well, I completed the download, and to tell the truth, playing with this demo software is about as exciting as watching someone else use a calculator. Still, I am tickled to death that I can start getting pressure readings. I got the following email from RSI. Hoping 99 others will soon have gotten it as well.

H. C.

Thanks for reserving a PressureTrace Device.

For reserving early you will receive glue and everything required to
equip 3 firearms with strain gages along with the PressureTrace module,
software and cables. You will not be billed until the product is ready
to ship. Save this email until we contact you again for billing
information.

We have no idea what the demand will be for this new product or if we
have ordered enough circuit boards and components. Initial production
will first be allocated to customers who reserved product in advance.
PressureTrace will not appear on our shopping cart until all advance
orders are filled. If reservations exceed the initial production, more will
be made, but this will cause a delay of a few weeks. Advance orders
will be given priority for available product based on the order in which
they were received.

If for some reason you change your mind or will not be able to complete
the order please let us know so we can allocate the PressureTrace
device you reserved to someone else.

Thanks again for your support.

Jim Ristow
Recreational Software, Inc.

DONE.

I can't wait to see what my rigs are running.

Thanks for the heads up on this Henry. I've reserved one, and I look forward to trying it out. - Dan

What's about Kolbe's recoilometer ?

Kolbe P MAX works fine with minimum of works ( just screw the accelerometer ring on the scope or on the barrel with an adaptator )and enter parameters but give you only max pressure , that enought for 99% of load dev with safe , the trace of pressure is use only to compare primer effect or engraving effect but most of time you need a accurate triggering to link time axis to bullet travel and read pressure curve is not so easy except the max pressure .

Strain gage system give a curve BUT some parameter are very important

strain gage location :
following the thread lenght you are not always at the same place on the chamber ( not same steel thickness )
number of strain gage
strain gage is not accurate as two strain gage set at 180� ( half bridge ) or 4 ( full bridge
) set at 90� .
temperature of use :
temperature factor is very important because strain gage is a resistor sytem resistance vary with temerature and need to be compensate .
strain gage quality :
strain gage is a electronic components with tolerance and accurate strain gage are made by company as Vishay or HBM but cost is more costly that cheap one from OEM .

best is to make test with factory loaded ammo and get some trace first , before to make load dev that can give you interesting info .

good shooting

DAN TEC

Strain gauge devices will only give you RELATIVE pressures in the same gun. Estimates of the correlation of relative pressure from a strain gauge system to absolute pressures are hardly more accurate than "reading" primers or measuring case head expansion.

It is an interesting diversion, and WILL tell you whether the load of 4350 generates more or less pressure (in your gun) than the load of H-414, but don't be deceived into believing that you can make an accurate representation of absolute pressure expressed in PSI, CUP, KPA or any other measurement. Only when the barrel steel is of a know thickness and elasticity and the chamber is of a standard size can a strain gauge measure in absolute terms.

Stonecreek--With the program that operates this guage as well as Oeler's, you put that case size,
case thickness,
and barrel thickness info into the equation and it gives fairly accurate actual results.The pencil
and paper formula can do this with old strain gages, and they just incorporated those in, so computer does it all.Ed.

I ran the precision stats for Southwest, and can tell you that the PressureTrace is very precise. Burt at SWP did a very nice job, and the system is well thought-out. You will be happy with it.

Strain gauge systems do give a good estimate of absolute pressure. You have to remember that all measurement systems contain error. The only issue is how much they have. The "relative pressure only" bit is legal boilerplate, at least on the two systems I have.

Fer Pete's sake look at the error in the copper crusher system. For a hundred years or so, they thought they were really measuring PSI. Along came modern instrumentation, and they found out that they were miles off base. It is just good luck that for high pressure systems, copper crusher numbers are usually less than true PSI numbers. Still, the system served us reasonably well for a long time. You just have to be careful to estimate the amount of error, and respect the fact that no measurement system is perfect.

I don't have a web page to put photos up, but if someone wants to do it for me, I can show you what the system looks like. It's about the simplest little box you can imagine. The laptop computer is where most of the action is.

I also just put one on reserve. Should be pretty interesting to see how it all works.

Turok

Denton,
Do you see a problem with hooking up the Oehler M43 and this Pressure Trace device to seperate strain gages on the same rifle for simultanious testing? I'm reserving one too.

You definitely can put two separate strain gauges and two separate pressure measurement systems on the same barrel... no problem.

I'm going to get a chance to do the stats on the Oehler fairly soon.

As nearly as can be determined from available data, the PressureTrace is much more repeatable than the CUP method, and more repeatable than published piezoelectric PSI data.

Some of the problems with strain gauge systems that were mentioned earlier are easily overcome. For instance, the PressureTrace resets its zero before every shot. This washes out error due to thermal expansion of the barrel. As I said, its very well thought out.

I have an article coming out in the July Varmint Hunter on the repeatability of various shooting related measurement systems. The article was written a few months ago, before I saw the PressureTrace. I just sent them additional material on the PressureTrace, which they will probably add to the material they already accepted. They have also asked me to do an additional article on how to set up the system, and work up loads. That should appear this fall. Those of you who are getting systems: Be sure to let me know about your experiences.

The adhesive you use to apply the gauge is critical, as is your application technique. A tube of the correct adhesive comes with the system. JB Weld also works quite well.

For the next rifle I instrument, I'm going to put the gauge on the side of the barrel, a little below center. Then I'm going to cut a small pocket in the top of the stock, next to the barrel. The teeeny little connector can comfortably ride in the pocket, out of the way until it is needed.

To reduce the possiblity of placement error I am going to try some triple bridge gages. Once I find a load that is super consistent, I'll hook the box up to the triple and compare, probably won't be much but would be interesting.

Roger...

I think you'll have problems doing that. The circuit is designed to hook to a single gauge, with the necessary fixed R inside the box. Also, I don't think that it is necessary. The system is already more repeatable than the published piezo data I have access to, and piezo has shown itself to be adequate.

At normal barrel temperatures, the tempco of the strain gauge is small, so using advanced strain gauge techniques offers little improvement.

As I said, Burt has really thought this one through.

Denton,
Does the Pressure Trace come with a provision for calibration to PSI? My experiences with the Faber Unit lead me to agree with StoneCreek's post on relative Strain Units vs PSI measurements. In fact, I just spoke to a friend that also has the Fabrique Unit who was perplexed that his psi conversion was not matching up with the yield when he had the opportunity to send his ammo out to be measured via Piezo (about a 10Kpsi difference).

On the other hand, brief conversations with Jim R lead me to believe he's addressing that somehow via the software(?) I'll be calling him to get more detail on that as I can't imagine how.

[ 04-29-2003, 21:58: Message edited by: Chris F ]

Chris...

That is a perplexing subject. I'll do the best I can with it:

The short answer is that the PressureTrace does draw a pressure curve, with the vertical axis labelled directly in PSI.

The PSI reading is derived from the basic equations relating expansion of the OD of the chamber (strain) to the force applied by the pressure of the gas (stress). Those equations are pretty well known and widely accepted as giving good estimates of pressure.

Of course, the PressureTrace unit carries the usual "relative pressure only" disclaimer, as it should.

You could probably figure out some kind of hydraulic setup that would pressurize the chamber, and that would be calibrated in fundamental units, such as a known weight. But that seems awfully messy.

I've never sent ammo out for pressure testing because the results aren't going to get you an answer. A little longer or shorter leade, a slightly tighter or looser chamber, and a few tenths of a thousandth difference in bore diameter can add up to a major difference in pressure readings between two barrels, using identical ammunition.

Commercial testing labs use test ammo, so they can verify that they are all getting the same reading from the same ammo. But, unless they have some secret I don't know about, all they have is repeatability--and a relative measurement that they believe is also accurate. As nearly as I can tell, they don't really know for sure, either.

The technique for applying the strain gauge is critical. There is a certain "roll of the thumb" needed to make sure that the whole gauge is firmly epoxied to the barrel, without any air bubbles or gaps. I like using JB Weld, because it sets slowly. A taut piece of electrical tape over the gauge while the epoxy sets generally "snugs it down" correctly. I don't know, but it is possible that your friend had a problem with gauge application.

My Fabrique unit consistently gives numbers that are very believable. I tried some of the Federal High Energy cartridges in my '06, and got very plausible 58 KPSI readings, with fairly wide swings, and SLIGHT bold stickiness on the very hottest of cartridges. That seems about right.... 58K is the upper spec for the '06. Super X's ran quite a bit less pressure. My instrumented Mosin M39 also gives very believable pressure readings.

What you CAN'T do is calibrate by making up some loads that have published PSI specs (I tried!). As nearly as I can figure this out--and I'm still working on it--they fire cartridges made up with several different lots of powder, and publish the pressure and MV numbers from the hottest lot, in a tight chambered test barrel. That would be a good, conservative thing to do. But the problem for you and me is that we generally have no idea how hot our particular batch of powder is, compared to the rest, and we don't know the effect of their different barrel dimensions.

BTW, the readings from my Fabrique and my PressureTrace average the same, with the PT being more consistent (repeatable).

Whew! Long discourse. 'Scuse the verbosity.

Anyway, my bottom line is that I think the careful home experimenter can produce pressure readings that are at least as repeatable as labs do, and probably about as accurate. Since you can't fully depend on that, though, it is best to err on the side of safety and just call the readings relative.

If you want to shatter your confidence in commercial labs, plot the piezo data from page 91 of the new Lyman reloading book. There is a statistically demonstrable upward trend in the data vs time, and it is not a small error. Whoever took the data was not allowing the barrel to cool sufficiently between shots. Barrel temperature is a very important variable in chamber pressure. Also recall the for a hundred years or so, people thought they were measuring PSI with the copper crusher method.

Denton,
Thank you for your reply.

I had hopes that you knew something about the PT that I didn't on the calibration to PSI.

I had advised my friend of the same regarding the bonding of the gage (and also the alignment of the gage to bore centerline avoid a cosine effect).

Another area where I feel that the PT and Fabrique units have advantages over the Piezo and Copper Crusher methods is related to what you highlighted. We can take pressures off the actual barrel we're using and not have to transpose data off a pressure barrel (which due to many variables is not perfectly the same as ours).

Another Question; I've notice that the PT gages are tiny compared to the one that Faber was supplying. Any comment there, and are the larger gages still usable (with proper connectors) with the PT?

The Fabrique gauges are useable with the PT device. I made up a little adapter with a Fabrique connector on one end, and the PT connector on the other, and very easily used my old gauges on the new system. The PT connector is a small two-pin job, probably out of some computer application.

The gauges I got from Fabrique came in their original manufacturer's packaging, with a gauge factor on them. You just enter the gauge factor in the PT software, and you're on your way.

Chris F and denton:

What is this Faber or Fabrique device? I am mostly interested in the cheap strain gages, because after the third one, RSI charges quite a lot for theirs. Would any similar sized strain gage of a similar factor work just as well?

Thanks,

H. C.

Good idea henry. A source of relatively inexpensive strain gauges would be great, especially for us gun addicted types. - Dan

Steve Faber was selling a strain gauge based pressure measurement system for about $150, through his company, Fabrique Scientific. It was a pretty cool little system, and I use mine a lot. It produces only a peak reading, in microstrains, which is easily converted to PSI.

As I understand it, Fabrique is no longer selling this product.

The new product, manufactured by Southwest Products (www.swproducts.biz), is $189, and works in conjunction with your laptop computer. It draws a graph of PSI vs. time, and automatically captures the peak reading. It also stores your traces, and is more repeatable than the Fabrique unit.

Burt, the guy the developed the product, does do some sort of individual calibration on his strain gauges.

The Fabrique product uses a strain gauge produced by the Micro-Measurements Division of Measurements Group, Inc., Raleigh, NC. Any gauge with the correct resistance and gauge factor should work just fine.... 350 ohms, GF = 2.

A raw strain gauge comes with no leads, and no connector. So, if you have to take care of all that, it is worth something to have someone do all the prep work for you.

Denton,
thanks for all the insight. Just to clarify a couple things though, and I'm not sure if you're familiar with the Oehler 43 gages or not, but they are really small and easy to hide under the barrel. They also have two solderable contacts on the gage for the leads, the gage factor is also 2.095, so should these work with the PT unit too? They are much cheaper gages and I have plenty of glue, etching acid and neutralizer to last a long, long time.

The gages are from MMD also, it says they're type CEA-06-250UW-350, they come in a box of five and are 350 ohms too. Seems like I could keep using these doesn't it?

Can the PT system be converted to use a telephone type connector like the Oehler does so I have all the same connector types? I'm guessing it wouldn't be a problem?

Is the PT software pretty basic and simple? It looks like it is. My dad, he just don't do well after a few key strokes, he gets confused just "looking" at most of the stuff on the Oehler with what it does.
When I even mention computer something or another, I think the first thing he thinks is "he just lost me". He gets around on the internet though. Barely, and that's it. He don't do email. If he can't see what it's doing and why, I think he gives up on trying to figure it out. Mechanicing is his thing.
Thanks again.

That is exactly the strain gauge that the Fabrique unit uses, and I have successfully used them with the SW Products unit, so there should be no problem. When you set up a new barrel, just enter the gauge factor printed on your box of gauges. Mine happen to be 2.09.

I can't see any physical difference between this gauge and the one Burt used in the new system.

The software is very easy to use, if you just want to collect traces. The first time through, you plug the unit into the serial port, and turn it on. Then you run the setup. You do have to click OK after it finds the right port, and data rate. Once it is installed, you just run it. It comes up with a "shoot" button at the bottom. Click that, and every time you do a shot, it will collect a trace and display the peak pressure. Just keep on shooting until you have as many traces as you want. When you are done, you just tell it to stop and save the data.

The Fabrique unit cable has a telephone connector on one end, and a little 3 prong connector that seems to be from the model airplane/model car market, on the straing gauge end. I just made up a little pigtail that adapts the 3 prong Fabrique to the 2 prong connector on the end of the SW Products cable. Works fine. Lets me use either unit.

I can tell I will have to buy a couple extra batteries for my computer.

Thanks again Denton. I think I remember seeing a connector on the Fabrique, might be a "J" connector used in RC airplane batteries and servos now that you mention it, got some in a box somewhere. It's nice to know what to expect ahead of time. Thanks again.

Roger,
I bought one of them 12v battery booster for jumpstarting your car that has accessory plugs on it for use at the range with the cig lighter charger.

Denton,
In my correspondence with Jim R, I got the impression (perhaps mistakenly) that the Pressure Trace could be used as a "stand alone" device at the range without the computer. And that the data captured could be downloaded and processed at home.

I haven't gotten to revisit that with Jim yet, but others have since told me that it's like the Oehler in that you need the PC hooked up to capture the data.

Can you clear this up for me? That would definitely affect the usefulness and practicalities of the PT for me.

The PressureTrace unit has no memory or CPU. It has an ultra-low noise amplifier to bring the millivolt or so signal up to a useable level, an A-D converter, and a serial interface.

A lot of the work went into the software, which handles most of the "chores".

Unfortunately, that does mean that you need the computer on, and hooked up to take readings.

The Fabrique unit is completely self contained, which makes more "handy". All the same, I expect to do most of my future work with the SouthWest Products unit. It's just a better system.

Ooops.... it does have a PIC CPU, but no ability to memorize trace data.

I sent an email to RSI, and it looks as if these will be coming out on schedule:

(the part of my email they left in their reply):
>I'm just curious how close to 100 units you are. Is
>June still the estimate?

(their reply):
Henry;

It looks like we may sell all 100 before they ship. It will be
close. I have around 75 reservations and still counting. We will
reorder more circuit boards because it looks as if this product is
going to be a big hit. That will help get more together in short
order.

I did not want to over promise on the delivery date in the event we
ran into a back order issue on a component or got bumped off a
production line by a bigger order. So far everything seems on track
and we may be able to start shipping at the end of May, certainly
early June at the latest.
--

Jim Ristow
Recreational Software, Inc.
Email: rsi@commspeed.net
http://www.shootingsoftware.com
"Better shooting thru computing"

I tell you what...this is going to embarass alot of folks when they take a look at their pressures.
I am LUSTING to find out what pressure my .500 A-Sq is making at the max velocity.

I just thought of another interesting application for this device that I had not previously considered. My shotguns.

I have wanted to experiment with slug loads, but data is scarce. Also, warnings that come with shotgun loading data are that much sterner than the warnings about changing components for metallic cartridges. Now I think I'll have something that allows me to experiment.

Any day now, I expect.

H. C.

It came UPS today. RSI was short of strain gages, so they shipped the device with one gage and will send me two more gages later. They emailed me and asked if that was alright. It takes 24 hr for the adhesive to cure, so I won't have any data until at least this weekend.

H. C.

Henry,

I'm using an Oehler 43 and wondered what the deal is with applying the gages to the barrel on the PT gages, location and procedure recommendations they give you?

Is the gage flat on top or does it have soldered leads already on it?

The gages I get for the Oehler are flat and you lay them down on the plastic lid on the container they come in just the way they'll set on the barrel, then use a special Scotch tape and stick down over the top of it as a means to handle it without getting it contaminated.

Position the gage in the predetermined location at the mid-way point between the face of the reciever and the cases sholder.

Tape it on and fold back the tape and gage on one side until the gage is layed back upside down and just all the way off the barrel, about a 1/4" gap between the edge of the gage and the barrel where one long end of the tape is still stuck on.

After the bbl has been degreased well, an acid etch applied with a Q-Tip and wiped off before it dries so it doesn't leave any residue.

The neutralizer is then aplied in the same way too.

Now you apply the super glue accelorator to the gage only and then two drops of glue to the point where the tape holding the gage meets the bbl. IMMEDIATLY use a tissue or paper towel to squeegy the tape and gage down as the glue flows under the tape and gage in an even way from the sqweegie action. Hold firm even pressure on it for a minute or so and it's on. Peel the tape back at a steep angle, almost layed back flat on the barrel so it doesn't pull the gage off.

Solder the leads onto the contacts and crimp on a connector and your all done.

I'm wondering how you can get an even thickness of glue on under the gage, which is important, if they already have the leads soldered on top. I'm sure they have it figured out, just wonder how they accomplish it so well.

You can get the gages from Oehler for $40 and you get 5 in a box too. Make and solder on the leads is the only thing you need to do. Much cheaper than what they charge for 3 gages too. Takes about ten minutes to heat up and solder the wire on is all.

I got the email from Jim on the 5th saying they were availible now, all I need to do is go back to work to get into one.... a week or two off I'm told. Let me know how it works out.

Brent,

There are detailed instructions here.

http://www.swproducts.biz/PressureTrace/PressureTraceDoc/Strain%20Gage%20Installation.htm

The gage look like this:



The gage is on a piece of brownish tape. The brownish tape is 1/2" wide and 1 1/2" long. According to the instructions, the whole piece of tape stays on the gun with the gage.

I haven't started trying to install it yet. Maybe this weekend. Won't be mowing the lawn with all this rain.

H. C.

My pressure Trace has shipped! I emailed Jim and he said they went out on the 11th Priority Mail (to me here in Alaska), also the extra strain gages went out this past Wednesday.

I cannot wait to get this on my .500 and another on my FAL.

I ordered mine as well. I haven't heard anything about it shipping yet, but I sure am excited to see it arrive. Too bad I wont get to play with it until the end of August.

Turok