PROVING RING CONSTANT

[avinashcivilengg]

HOW TO FIND PROVING RING CONSTANT, AS I READ MANY POST THEN I COME TO KNOW THAT BY PLOTTING GRAPH IN BETWEEN STANDARD LOAD TO THE READING OF PROVING RING, AFTER THAT FIND THE SLOPE OF THAT LINE, SO MY ANOTHER QUOTATION IS WHICH VALUE SHOULD BE ON X-AXIS AND Y- AXIS PLEASE HELP ME BECAUSE WE WILL GET 2 DIFFERENT SLOPES WHEN WE WILL INTERCHANGE THE VALUE

 

[Ron]

Your graph should start at the origin of the two axes. If you have zero load, you have zero deflection of the proving ring. Add load in consistent increments. For example, if you expect a total load of "X" then do increments of 0.1X. This should give you a reasonable plot of load vs. deflection of the proving ring. Sometimes you will have two different slopes....one for a low load increment, one for higher loads. That depends on the stiffness of the proving ring.

 

[avinashcivilengg]

i was started with 3,4,5,6,and up to 10 kg and noted the deflection from that i got 1.27 valu i.e slop value and as mentioned on proving ring its limit is about 2kN SO plz suggest me that ans which i got is it correct or is there any another method that i have to adopt

 

[oldestguy]

As to which should be ordinate or abscissa, as long as you know which is which for your plot, you only want a multiplier to use with the deflection measurement of the dial. How you arrived there is not important. I'd prefer the dial reading on the ordinate.

 

[avinashcivilengg]

what about my ans is it correct?

 

[Ron]

I can't tell from the data you provided. Give us both the load and proving ring deflections.

 

[avinashcivilengg]

i'll send u a exel sheet

 

[oldestguy]

If this data is on a spread sheet, why not use that instead of a plot?

Column A has load numbers.

Column B Has dial readings corresponding to the load numbers.

Column C has corrected dial readings by subtracting initial dial reading from Col. B.

Column D divides Col A by Col C

At the bottom of the data entries compute the average of values in Col. D as the calibration factor for the proving ring.

 

[avinashcivilengg]

exel sheet

 

[avinashcivilengg]

formula is like (proving ring constant* proving ring reading right) and 1 div means 1 number which calibrated on big diametrical scale is it right

 

[oldestguy]

At first I thought the low precision of the reading of deflections was too crude, but perhaps for higher loads it may be sufficient. I'd prefer a calibration to be straddling the range of loads that later will apply to the use there of. Maybe that 1.4 is really 1.400??? The range of loads for calibration is very low for the reported load range capability of the ring. Using seven of the data points and my suggestion of layout, I get average calibration of 1.438, assuming the data of load and dial each is read out to three significant figures. If not, the work can only be assumed as very rough calibration, not good for much reliability. Per Ron's comment there are at least two different slopes.

 

[Ron]

Agree with OG....I think you have a precision issue. Your curve looks good, but for most proving ring applications, your deflections should be measured in 0.0001" increments or a corresponding metric accuracy.

Also, you should not have a "Y" axis intercept, even with your trend curve (straight line). Zero load is Zero deflection.....

 

[oldestguy]

In order for a proving ring to have any validity, the calibration should be against a method that has very good precision. This might better be a mechanical scale that uses known weights, no springs, no strain gases, etc. If you have a testing machine that you know is correct, maybe yes, depending on your use of the proving ring.

 

[Ron]

OG....we had our compression testing machines calibrated every year to NIST standards with traceability. We did the same for our major proving rings. For the minor proving rings, we did a secondary calibration from our testing machines with a known, calibrated load. We also did secondary calibrations for our hydraulic jacks for load testing. You are correct as usual!