早在1900年，当使用金属硬度测试作为一种质量保证措施时（确切的钢硬度）砝码式硬度测试系统就被用于施加所需的试验力。原因很简单，砝码式硬度测试系统便宜且易于制造，且能满足当时硬度测试的精度要求。
然而，砝码系统的问题是试验力必须通过杠杆结构施加在试样上，并利用大量的活动部件得到最终的小压痕。将砝码系统产生的试验力转移到小的金刚石压头或球压头顶部是这很难实现，如进行洛氏HRC测试时需使用150kgf的主试验力。一个便携设备很难满足大尺寸和150kg的力，它要求设计者利用更小的砝码和杠杆来放大试验力。
对于进行3000kgf的布氏测量此问题会更为严重，同时，对于小力值硬度计，如需要达到1gf是，也是一个挑战。
杠杆需要支撑、导轨、轴承和其他产生摩擦的部件，这些部件会导致受力不稳定。
虽然这些偏差的源头可控，但系统中的任何摩擦最终都会产生不利影响，并在仪器的使用过程中越来越严重。同时，在砝码系统中很难控制试验力，因为要通过移动砝码得到所需的试验力，然而在没有过载或震荡的情况下是很难快速停止的。许多老的硬度计使用缓冲器（充油阻尼器）来控制，然而，缓冲器本身就存在如漏油，磨损，密封，温度影响等问题。因此，在后来的设计中，缓冲器被马达取代了。
尽管一些阻尼缺陷消除了，但快速测量的要求则对马达速度要求更严苛，所以，试验力过载和波动问题经常出现。电动砝码式硬度计的工作速度慢，不适合生产。一般认为，砝码系统的试验力是保持一致的，但这种假设很难实现。
因为最终施加的力是无法控制的，所以你可以称之为开环力加载系统。
砝码（开环）系统的优点：
– 制造简单
– 造价低
– 模拟系统，无需供电
砝码（开环）系统的缺点：
– 无法反馈实际的试验力
– 对温度和环境较敏感
– 测量重复性和再现性差
– 机械加载系统复杂且不便维修
– 机械结构易磨损
– 维护费用相对较高
考虑到砝码系统的缺点，INNOVATEST 轶诺所有的硬度计都不是砝码系统，而是闭环传感器控制系统。 闭环传感器控制系统的优势，下篇文章进行介绍。
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
