31. Supplements
Characteristic of Electromagnetic Exciter (detector) used for Cantilever method
1. Impedance characteristic of electroMagnetic Detector
The outer shape of MP-0910 and M-0912 is same. |
Measurement method
Measure by 2 kinds of electroMagnetic Detector (dC resistance value: MP-0910- 850 to 950 Ω, MP-0912- 85 to 105 Ω). A 1 Ω cement resistor is inserted into the electroMagnetic Detector series, current is detected, and the frequency response function with voltage is measured. Refer to Figure 1.
As a result, it can be seen that the impedance changes considerably. MP-910 and MP-912 are almost parallel. When MP-910 is used, the impedance is higher, so it is necessary to pay attention to the impedance of the connected instrument. When it is used as an electromagnetic exciter, a normal power amplifier is expected to have insufficient excitation power. It is thought that the impedance decreases in the high range due to the capacity components of the coil.
Fig.1 |
2. The measurement of vibration velocity response and linearity for electroMagnetic Detector
The measurement diagram is shown in Figure 2.
The vibration velocity response is shown in Figure 3. (frequency response function with laser vibrometer) The frequency characteristic is fairly flat, however, this is considered to be due to using a weak mounting jig judging from the sensor performance (not using as exciter) and no reaction power.
The linearity with respect to the vibration velocity is shown in Figure 4 to 7. It turns out that MP-910 and MP-912 have sufficient performance for loss factor measurement. The normalized velocity is a value obtained by normalizing the maximum output measured by each detector as 100% as the output voltage of the detector is very sensitive to the detection distance from the iron piece.
Fig.2 |
Fig.3 |
Fig.4 |
Fig.5 |
Fig.6 |
Fig.7 |
