Discussion in 'Strings' started by Leutonio, Oct 16, 2007.
Someone has it? Someone knows how to use it?
I have one of these. Once I've strung a rqt, I test the stringbed and include the readout on my frame sticker that I put on every rqt I do.
Basically you attach the ERT300 to the centre of the stringbed and press the yellow button. It will then send out vibrations and then show its reading on the LCD screen. The measurements are given in DT's or dynamic tension. In essence it measures the stringbed stiffness and not the actually tension.
Using this tool, one can follow the tension loss of the stringbed and inform customers when a restring is needed. Its handy as it fits in my rqt bag so I can take it to the courts and check their rqts.
Paul is spot on with his comments. I always attached the top clip of the ERT on the 8th cross string, just to add consistency to the measuring process.
Thanks but if i need to know the actually tension for example after i've strung a racquet at 25kh/24kg what should i'll do?
Can i measure with it the tension or not?
No. The only device that pretends to measure actual tension now out is still the Stringmeter--and, because of difficulties related to this, the manufacturer has switched to advising you take a reading immediately after stringing and then track tension loss, instead, too.
It doesn’t measure tension directly--it measures the stringbed stiffness overall--but that number is directly proportional to the average tension in the strings of your racquet.
So, the manufacturer includes a calculator with the device, that you can use to look up the “Dynamic Tension” (DT) number that the device measures, in order to get the average string tension in the strings on your racquet.
Like Valjean said, don't expect the Stringmeter to give you the true tension, either. It's all relative. For example, if I string 60 lbs, I don't usually get a 60 lbs reading on the Stringmeter right after I'm done stringing. Usually I get a bit less. So you gotta take the measurements over time and chart out the data points relative to each other to guess what the loss is. And the readings are not that consistent, either. On top of that, I just hate the idea of bending the heck out of my string to get a reading each time.
I don't know of any device that can give you the actual tension reading on what you pull. The best way is to measure the stiffness of the stringbed because this parameter correlates with the string tension.
The actual way to measure stringbed stiffness is to see how much force it takes to depress the center of the string bed by 1cm over the contact size of a tennis ball. The resulting reading is call the DT (dynamic tension). This reading is actually more desirable to know than just the string tension pulled because it combines all other factors, like your string type, string gauge, string tension, string pattern/density, etc.
I think the more expensive machines like the Babolat do the measurement by literally depressing the stringbed and see how much force is applied. But these things cost a few grands.
The cheaper devices like the ERT300 'simulates' this action by putting out a vibration on the stringbed and electronically measures the harmonics of the vibrating strings and performs calculations with this data through some built-in equations to arrive at an estimated DT (dynamic tension) reading.
There's also another free method called 'freqmess' (do a search for threads on this), where you strike the stringbed to make a sound and record this sound into your computer. Then you input a number of different parameters into this free program called 'freqmess' and it enters all that data, including the harmonics of the sound recorded into an equation, and calculates what the tension is based on this.
I tried the Stringmeter first. Then I tried the Freqmess approach. But I wasn't happy with either for various reasons. So I ended up buying the ERT300 and I'm happy with it. I use it to take DT measurements from my racket after every other playing sessions and the readings seem pretty accurate and consistent. I organize the data into an Excel spreadsheet and plot out charts of the DT readings. And based on this, I monitor my DT loss and decide when I should restring.
This is a less expensive variant: http://eagnas.com/maxgen1/etest.html. When properly combined with the Stringmeter, which can measure each individual string as well, you can get a pretty reliable picture of what you want.
Can you post below your data for example. Thanks.
By the way, for those who don't know, the ERT 300's user manual is available for downloading at the site where it is usually sold.
There’s a public database where you can see lots of examples at the stringforum.net website.
It’s the stringforum.net DT Database and it’s an excellent resource for real world DT results with various combinations of strings, racquets, and stringers.
Here's an example of a chart I have. As you can see, there's an initial drop within the first 10 hours of stringing, then the DT flattens out, then dropped again after about 30 hours. The string broke at 50 hours. The first drop is probably just normal initial tension loss. The second drop at 50% is probably due to the elasticity giving out. I notice that after this time, my string started to move around more than before, until it broke at 50 hours.
Sorry for the extra white space at the bottom. I printed out my Excel chart as a PDF file and used the Zamzar website to convert to PNG and posted it on the Photobucket website. Somewhere along the line it picked up the extra space. If anyone knows of a better way to do this, I'm all ear. Thanks.
You can just use MS Photo Editor to edit and crop, like so:
FWIW, the stringforum.net DT database provides a graphical chart too, when multiple datapoints have been input, such as here:
Note that the shaded blue area at the left is time after stringing, but prior to play.
Thanks for the tip on MS Photo Editor, Gjoc. I'll definitely give that a try next time.
By the way, the Stringforum.net DT database was what inspired me to buy the ERT300. It really has some pretty good information there and the database keeps on expanding nicely.
I tried a couple of times to contribute my data there but for some reason it didn't take. So I got frustrated after a couple of tries and gave up. But it could have been my fault since others contributed to the database just fine.
I was going to go the Excel route myself, until I realized that they already had all that set up, and I could just use that.
They have a convenient feature where you can simply click on a “just show me my data” link to quickly find your own data.
I don’t know why you had trouble adding to their database, but one possibility, IIRC, is that they have it set up with two different/distinct userids (though they can be the same thing), one for the discussion forum, and one for the string database--everything can be the same, but you actually have to “register” twice, so that’s a bit confusing, imo.
is ERT 300 available in TW?
how much does it cost?
They’re $179.95 (and worth every penny) where I got mine, but no, TW doesn’t carry them.
You can find them on the Internet easily enough though--just Google the phrase (i.e., with the quotes) "ERT 300 Tenniscomputer & Racquet Diagnostics" and whatever link comes up at the top of the list should be fine.
thats a great post. where can you buy the ERT300?
I'm curious about the TW rule here. If they don't sell the item anyway, are we allowed to tell other posters where we bought that item? Or is it still prohibited?
But there aren't a whole lot of places that sell this thing in the US anyway. If you google it like Gjoc suggested, you'll find it, Zapvor. I bought it for the same price and probably from the same place Gjoc bought his. And I agree, it's a bit of money, but it's worth it, especially if you have a lot of rackets to keep track of.
If you string for other people, you can take a measurement for them in the beginning, and encourage them to bring it back for free measurement to know when they should restring. This should help with the repeat business. It's recommended that you restring when the DT value drops 10-15% of the original value, and not any lower than 28.
zapvor ... read the post above yours ... they are quite pricey and are 179 dollars
That was it. I remember now. I took the time entering my first set of data, only to learn at the end that it didn't take because it said I wasn't registered. I didn't realize at first that you needed to have a different userid for the string database. I just thought that I wasn't logged in or something. So I retried the second time and got the same error. Then I realized that it required a second id. By that time I was in a foul mood for wasting all that time, so I decided to forget it.
Yeah, that’s too bad, but I can see how that would happen.
You should definitely go back and get it straightened out though, because, other than that, they’ve done a great job and it really works well.
It really seems to be catching on, too--contributions to the database seem to be coming in faster and faster.
Also, FWIW, as far as checking the DT later, I put the DT right on the label that I put on the frame with the string(s) and tension(s), as someone else said earlier in the thread that they do too, so that when/if I check it later (whenever and wherever that might be), I have the original DT right there in front of me for easy comparison.
What I like about the claims for it is that the ERT 300 supposedly takes into account racquet design, head size and string type. This would make it unique among similar devices designed to do the same thing.
Question is, how well does it actually take those things into account???
Today i've received this ETR300 and i've immediately tried it on my 2 Yonex.
I have 2 Yonex RQIS 1 Tour 95sq strung with tecnifibre X-one 17 gauge
The first one has new strings and i've never used it.
The second one has used strings (about 5 hours).
I've measured both 2 Yonex.
The first one (new strings) score is 33 DT.
The second one (used) score is 35 DT.
How is possible? Please explain to me how the second DT value is higher than first value of the new racquet...
I don't think that this ability is anything special or specific to the ERT300 per se. RDC measurements from the Babolat RDC, for example, would cover to those parameters as well.
It's not so much about the instrument being smart enough to have knowledge about those special parameters. It's more about the kind of measurement (DT or RDC) values those instruments take are 'blind' to those parameters. Therefore, the value represents a 'universal' feel or representation of stringbed stiffness that 'inherently' takes into account all those parameters.
For example, in theory, if you have 2 same brand/model rackets with the same string type, strung the same way, same tension, etc, but one with a mid head size than the other with a mid plus head size, the DT readings between these 2 may differ slightly because the head sizes are different. So you can take that as the DT values 'take into account' that difference. Throw in all the other parameters, the same can be said that the DT values are different because they represent (or 'take into account') all those different parameters.
Hope this makes sense.
I have taken many DT measurements on many rackets. My observation is that on the exact same racket/string, most of the times, the data points go downhill, or stay flat, like they're supposed to. But once in a while (one out of 10 or 20 data points or so), there may be a stray data point that is one unit higher than the previous value (never 2 units higher, though).
I attribute this to the possibility that I didn't have the device positioned exactly at the same spot where I normally take the other measurements. Perhaps the string moves a little bit from the last time and caused the device to be off center a little this time. Or perhaps because the string is not perfectly symmetrical and I placed the device a little off to the left last time but a little off to the right this time.
Because of these small variations, some people prefer to take a few readings each time and average them out.
Once in a long while, when I got a really out of whack reading, it was always my fault because I didn't seat the device properly on the stringbed and one of the clamp feet wasn't rested properly on the string.
But overall, I find the ERT300 to give very consistent readings and if something is off, it's usually an indication that you did something differently (not necessarily wrong).
In your case, because they're not the same rackets, there may be even more variables involved. It may be possible that there was some inconsistency in the location where you place the device for reading on the 2 rackets. Or perhaps inconsistency in the way you strung the 2 rackets. Or maybe you tied the knots better on the used one and not as well on the new one. Or maybe this is an indication that your clamps are starting to slip a little bit when you strung your new racket.
So in theory, you're right, all things being equal, the used racket should have displayed a lower DT value. But I wouldn't worry too much about why the values are different at this point, and continue to take readings regularly for a while to see how it goes.
I'm not sure it does.
Here is what the user manual actually said: "All factors of influence such as racquet type, racquet size, string pattern and string characteristics are automatically taken into account.
DT (Dynamic Tension) is the *only* [emphasis mine] realistic (since close to play) and precise value that can be measured directly at the strung racquet."
And elsewhere: "DT is ball power in kilo pond (kp) required to depress the string bed 1 cm. at the sweet spot (ball impact)."
Now, only the ERT uses the kilopond measure. But the ERT 300 is accompanied by the "DT-disc" for converting its measurement value from DT to kp.
And the "DT-disc" requires a user to manually stipulate the racquet's head size before a reading can be arrived at.
I don't take the DT-disc literally like you do. To me, all it does is to give you a rough correlation between the DT value and the tension you string your racket at. The ERT300 doesn't require you to enter any head size data or string tension data or string type data for it to calculate what the DT value is. It could care less what those parameters are. There's only 1 button on the device. All you do is clamp it on the stringbed, push the 1 single button, and get a DT reading. So it's not that complicated.
The intention of the DT-disc is actually the other way around. You determine what 'mode of play, aka DT value' you want to achieve, and it gives you a ball park figure of what tension you should be stringing your racket at (based on racket size) to achieve that 'mode of play/DT value'. That's all it is.
So yes, the claim is true that it AUTOMATICALLY takes into account all the parameters. But that's the operative word, AUTOMATICALLY, just because the kind of measurement taken inherently is the end result that represents all those parameters. But it doesn't need to know what any of those parameters are.
Well, I’ll assume you read the directions and know that the measurement you’ll get is dependent on where on the stringbed you clip the device and how you hold it and so forth, and therefore, that you clipped it onto the same place on both and measured them both the same way...
So, the first thing is, the precision of the device itself is only quoted as being ± 1 unit, according to the manufacturer’s documentation, so your 33 could really be 34 and your 35 could also really be 34.
Having said that, in my experience the device seems remarkably consistent, so maybe the quoted precision has more to do with measurements made with one ERT-300 device compared to the same stringbed measured with another ERT-300, but nevertheless, ± 1 is the quoted precision.
Secondly, were the two racquets strung by the same person on the same day using the same machine set at the same tension? (You didn’t indicate that they were.)
If so, then thirdly, have the two racquets stayed together side-by-side through the same environmental conditions since being strung, or, for example, was one left in the car, or home in the a/c, while the other was used, etc.?
All of the above can cause variability in the dynamic tension. The fact that you now have a device that can measure/quantify the dynamic tension just means that you’re going to start seeing the results of the various differences, effects, and variabilities.
Now that you know that they’re different, and how much (only a little), you can start to understand/figure-out the “whys” of that.
Just to clarify, as far as the calculator disc that comes with the device, it does work in both directions...
The page of the manual that I posted above comes first and explains how to know the tension in the strings of a racquet that’s already been strung, based on it’s measured DT value (going from DT to pounds).
The next page of the manual, which I’ll post below, explains how to know what tension to string at in order to end up with a desired DT value in the stringbed (going from pounds to DT).
Since some amount of tension will be lost between the reference tension that is set on the machine and the tension that ends up in the strings after stringing (depending on the particular stringer and the particular machine and so forth) is why, “The experienced stringer will adjust the tension on his stringing machine accordingly” (from the tension value given by the disc), which is mentioned at the bottom of the page, when using the disc for that purpose (going in that direction, from pounds to DT).
I understand your clarification that the disc works both ways, but my point is that the practicality of the disc to me personally is only to know what tension I should string at to get my desired DT reading.
After the racket has already been strung, I could care less to use the disc the opposite way to 'guestimate' what the remaining tension on my string is, because I can simply just track the DT value and determine the implied tension loss via the DT values anyway. I wouldn't bother 'converting' the DT values back to estimated remaining tension and chart this estimated remaining tension data point. I would just chart the DT data points directly.
But actually, come to think of it, if I were a stringer and somebody came to me with a used racket without any prior DT history, and asked me if I can take a DT reading to see what the estimated remaining tension is, to compare it with the original tension he/she had it strung at, I can see the value of using the disc to do this conversion.
OK, point well taken.
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