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砝碼硬度計的特點|雙語
砝碼系統
早在1900年，當使用金屬硬度測試作為一種質量保證措施時（確切的鋼硬度）砝碼式硬度測試系統就被用于施加所需的試驗力。原因很簡單，砝碼式硬度測試系統便宜且易于制造，且能滿足當時硬度測試的精度要求。
然而，砝碼系統的問題是試驗力必須通過杠桿結構施加在試樣上，并利用大量的活動部件得到最終的小壓痕。將砝碼系統產生的試驗力轉移到小的金剛石壓頭或球壓頭頂部是這很難實現，如進行洛氏HRC測試時需使用150kgf的主試驗力。一個便攜設備很難滿足大尺寸和150kg的力，它要求設計者利用更小的砝碼和杠桿來放大試驗力。
對于進行3000kgf的布氏測量此問題會更為嚴重，同時，對于小力值硬度計，如需要達到1gf是，也是一個挑戰。
杠桿需要支撐、導軌、軸承和其他產生摩擦的部件，這些部件會導致受力不穩定。
雖然這些偏差的源頭可控，但系統中的任何摩擦最終都會產生不利影響，并在儀器的使用過程中越來越嚴重。同時，在砝碼系統中很難控制試驗力，因為要通過移動砝碼得到所需的試驗力，然而在沒有過載或震蕩的情況下是很難快速停止的。許多老的硬度計使用緩沖器（充油阻尼器）來控制，然而，緩沖器本身就存在如漏油，磨損，密封，溫度影響等問題。因此，在后來的設計中，緩沖器被馬達取代了。
盡管一些阻尼缺陷消除了，但快速測量的要求則對馬達速度要求更嚴苛，所以，試驗力過載和波動問題經常出現。電動砝碼式硬度計的工作速度慢，不適合生產。一般認為，砝碼系統的試驗力是保持一致的，但這種假設很難實現。
因為最終施加的力是無法控制的，所以你可以稱之為開環力加載系統。
砝碼（開環）系統的優點：
– 制造簡單
– 造價低
– 模擬系統，無需供電
砝碼（開環）系統的缺點：
– 無法反饋實際的試驗力
– 對溫度和環境較敏感
– 測量重復性和再現性差
– 機械加載系統復雜且不便維修
– 機械結構易磨損
– 維護費用相對較高
考慮到砝碼系統的缺點，INNOVATEST 軼諾所有的硬度計都不是砝碼系統，而是閉環傳感器控制系統。 閉環傳感器控制系統的優勢，下篇文章進行介紹。
DEAD WEIGHT SYSTEMS
Since early 1900 when the use of hardness testing of metals came as a measure to assure
quality (a certain hardness of steel) hardness testing instruments have used dead weights to
apply the required test forces.
The reason for this was fairly simple, because dead weights are relatively inexpensive and
easy to manufacture to the degree of accuracy required by commonly used test methods.
The problem of deadweights however is that the force must be applied to the test piece through a lever structure, with a large number of moving parts, to eventually a small indenter. Transferring the dead-weight force to the tip of a small diamond or ball indenter, for instance 150kgf main load used for a Rockwell HRC test, is difficult to accomplish. The large size and mass of a 150 kg weight would not fit in a handy instrument so it required designers to use smaller weights with levers to intensify the force to the desired levels.
The problem just gets bigger if the force increases to 3000kgf for Brinell measurements, but dead weight systems are also a challenge for designers for low force hardness testers going down to for instance 1gf.
Levers require pivots, guides, bearings and other friction-producing parts that cause force application instability.
Although it is possible to control these sources of error, any friction point in the system will eventually have a negative effect that slowly increases during the lifetime of the instrument. It is also not easy to control a dead weight application in a dead-weight system. Because the dead weight must be moved to apply the test force, stopping it quickly without overload and oscillation is problematic. Many older testers use dashpots (oil filled dampers) to control the application; however, these dashpots where source of problems on their own (oil leaking, wear & tear on the sealings, tempurature effects). In later designs dashpots where replaced by motors.
Although this eliminates some dashpot problems, the need to perform tests quickly makes motor speed critical, and as a result, force overshoot and oscillation are frequent problems. The motorized dead weight testers are also slow working machines, not realy suitable for production. It is assumed that dead weight originated forces remain consistent as each test is performed. But it remains to be an assumption, the reality shows plenty of problems.
Because there is no control on the eventually applied force, you could speak of an open loop, force application system;
Advantages of a dead weight (open loop) system:
Easy to manufacture
Low cost to manufacture
Analogue systems require no electric connection
Disadvantages of a dead weight (open loop) system:
No feedback on actual supplied test force
Temperature and environment sensitive
Low performance on Gauge repeatability and reproducibility
Complex & service sensitive mechanical force application system
Wear & tear on mechanics on a longer term
Relative high maintenance cost