两种测量技术的区别, 典型值图示

应变计测量是将测量体的弹性变形转换成应变电阻, 因此可以通过惠斯通电桥可以输出测量信号.

压电效应的基础是通过测量晶体在压力负载情况下产生的电荷来完成的.


图 1: 带有桥路的应变传感器

电荷然后通过放大器转化成相应的电压输出. 这两种技术可以互相弥补不足. 应变计有很好的长期稳定性和更好的线性.


图2,压电传感器原理

压电传感器 有更小的结构,并且具有更高的自然频率,非常适合动态应用.

当采用压电传感器测量时,因为石英产生电信号输出,实际上没有位移压电传感器的灵敏性通常不依赖尺寸和石英的体积,而是依赖使用的材料和几何形状.

Q = q11 · n · F

Q = 产生的电荷
q11 = 材料常数, 例如. 4.3 pC/N
n = 晶体的数量
F = 机械负载或力

采用应变传感器,塑性变形通常和胡克定律有关, 导致应变电阻的变化. 下面的等式表达了电阻的变化:

F = E · A · ε

ε = 测量体应变
E = 弹性系数
A = 测量体的截面积
F = 机械负载或力

∆R / R = k · ε

∆R = 负载下的电阻变化
R = 无负载的电阻
k = 应变计的 k 系数

通过比对应变技术和压电技术,在电灵敏度方面有很大的不同:

案例 1:
压电传感器 5 kN => 特性 -4.3 pC/N
应变传感器5 kN => 特性 2 mV/V=> 0.4 µV/N

案例 2:
压电传感器140 kN => 特性 -4.3 pC/N
应变传感器 140 kN => 特性 2 mV/V=> 0.014 µV/N

采用压电测量技术, 在附加的测量范围不会产生精度的损失.

应变技术有更好的长期稳定性, it is practically impossible to implement a test setup with infinite insulation resistance.

In practice, there is often a drift of about 1 N/min, which is why measurement has to be restricted to a few minutes, subject to the requirements of the measurement task. For a measuring range of 50 kN with 215000 pC, charge signal -4.3 pC / N and a drift requirement of <0.05 %, the maximum measurement time is about 25 minutes.

With strain gage based sensors, the full bridge circuit can achieve excellent linearity. This avoids having to compensate for additional interference effects such as temperature variations. It also makes strain gage sensors more suitable for high-precision measurement tasks in partial load areas,
such as for reference transducers. When space is tight and installation restricted, the piezoelectric sensor comes into its own. With the same measuring range and similar performance characteristics, the piezoelectric transducer is up to thirty times smaller in construction than a comparable
strain gage transducer.


图 3: 采用 MP85A-FASTpress控制器的压电测量链


There is room in measurement technology for both transducer technologies, strain gage and piezoelectric, for mechanical quantities. The two are complementary and where strain gage performance ends, piezoelectric performance begins. Piezoelectric measurement technology has been added
to HBM’s product line enabling us to always provide the optimum metrological solution.

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