What is Speed Verification?
There are many components of universal testing machines that are associated with speed measurements including the scale, dial, marked or unmarked recorder chart, digital display, settings, etc. Speed verification is a service that ensures these measuring devices are traceable back to a national or international standards laboratory, which means that devices used in the verification process have themselves been calibrated with adequate calibration standards. Verifications of testing machine speed consists (at minimum) of either or both of the following options:
1. Verifying the capability of the testing machine to move the crosshead at the selected speed
2. Verifying the capability of the testing machine to adequately indicate the speed of the crosshead.
Where applicable, the machine’s ramp-to-speed condition can also be tested. This condition can be significant especially when verifying fast speeds or testing conditions with very short test durations. This procedure will establish the relationship between the actual crosshead speed and the testing machine’s indicated speed and/or selected speed setting. Please note that ASTM E2658 cannot be used to verify cycle counting or frequency related to cyclic fatigue testing applications.
Do I Need to Verify Speed?
Some test methods define certain testing speed and speed accuracy requirements, and some do not. While the particular testing speed chosen is not always a critical parameter, it is also good practice to ensure that the testing speed is constant, stable, and repeatable. These reasons alone cause many users to request speed verifications of their testing machines. Other applications, where it is known or suspected that the material or component being tested is strain-rate or speed sensitive, are also candidates for requiring speed verification. Some examples include composites, carbon-fiber composites, ceramics, and liquid crystal polymers.
If you are required to report test speed with your results or are concerned about the consistency of results between machines or over time, good practice indicates that the machine’s speed should be verified. There are some applications where none of these issues are a concern, and in these cases it is not necessary to pursue speed verification.
What are the Basic Requirements of Testing to ASTM E2658?
ASTM E2685 requires that speed sensing devices are verified at least once per year as a system, in place, and operating as in actual use (except that during verification there should be no specimen installed in the machine). Reference standards used for the verification of speed measuring systems should have an uncertainty equal to or less than 1/3 the allowable error for the measuring system. The estimated measurement of uncertainty of the reference standards should have a confidence level of 95%.
Verification consists of at least two runs of data per selected speed, and at a minimum, the most commonly used testing speeds should be chosen for verification. System verification is invalid if the speed sensing devices are removed and checked independently of the testing machine, and if any speed sensing device is adjusted during the verification process, all tested speeds must be re-verified unless it can be demonstrated that the adjustment did not affect other speed settings. Likewise, verification is required immediately after any repairs are made to the testing machine that might in any way effect the speed measuring systems. (This does not include replacement or repair of printers, monitors, modems, or other such components.)
Can Instron Verify my Machine to ASTM E2658?
Yes. Instron is at the leading edge of test machine calibration and verification and was an active participant in the development of ASTM E2658. Instron offers two different services for speed verification to ASTM E2658 (these services are combined with displacement verification to ASTM E2309).
Standard Verification:
Instron’s Standard speed and displacement verification meets all ASTM requirements by providing:
- Verification of 3 customer-selected test system speeds via 3 data runs
- Verification of any displacement range between 0.8” and 40” of total displacement
- For this verification service Instron will verify 5 total points between 10% and 100% of the displacement range desired.
The standard speed verification measures the average speed between two positions. The crosshead or actuator is allowed a short time to accelerate to the set speed before an accurate time and displacement reading are taken. A second set of time and displacement data points are taken after a specified travel or time (typically 2-4 inches or 30 seconds). These parameters are used to ensure a high level of accuracy in the speed measurement. This verification will tell you how closely matched the actual speed is to the set speed when your system is under no-load conditions. It will also determine repeatability, as this test is run three separate times. The initial velocity profile of the crosshead, minute fluctuations of speed during distance traveled, or speed accuracy under loading, will not be characterized.
Enhanced Verification:
Instron’s Enhanced verification for speed and displacement exceeds the requirements of the applicable ASTM standards and mitigates additional risk by providing:
- Verification of 5 speeds total
- 3 customer-selected speeds for the most commonly used test speeds via 3 data runs
- Verification at 1mm/min and 1270 mm/min to ensure verification of reasonable minimum and maximum test system speeds
- Verification of any displacement range between 0.8” and 40” of total displacement
- For this verification service Instron will verify the customer-specified range from 1% to 100% of the displacement range. Instron will verify 5 points per decade of measurement.
Though ASTM D2658 only requires two data runs, both our Standard and Enhanced verification services perform three data runs. This is because three runs are required to determine the repeatability of measurement. Repeatability results are reported on your verification certificate.
Do I Need Enhanced Services if the ASTM Requirements are Met with the Standard Service?
Instron's Enhanced Verification Services are helping organizations mitigate additional risk by providing additional and more thorough verifications. This service may benefit you if:
Your testing methods change frequently. If new test methods are frequently being written, you may be at risk of collecting data at speeds you haven't had verified.
Your requirements change frequently. If your testing standards or auditing entities are frequently changing or becoming more strict, additional speed verification may help prevent unwanted interruptions in your testing.
You collect test data near the boundaries of your verifications. If data is being collected near the boundary of your most recent verification, you may be at risk of capturing data that falls out of the verified range.