This measurement column addresses frequently asked questions received by our customer support center and provides answers to those questions.
Our company offers two types of accelerometers: preamplifier-integrated accelerometers and charge-output type accelerometers. Because charge-output type accelerometers do not have a built-in preamplifier, they are suitable for measuring shock vibrations such as those encountered in collision and drop tests, as well as vibration measurements in high-temperature environments. When analyzing the charge signal output of a charge-output type accelerometer using analysis equipment such as an FFT analyzer or data station, the signal is converted to a voltage signal using a charge amplifier or charge converter before being input to the analysis equipment.
A charge amplifier is an amplifier that converts the charge signal output of a charge-output type accelerometer into a voltage signal. Typical charge amplifiers allow you to set the sensitivity of the accelerometer and set the output sensitivity (range) independently of the detector's sensitivity. Some also include LPF (low-pass filter), HPF (high-pass filter), and accelerometer signal integration functions.
Regarding the settings of the charge amplifier and analysis device
Our CH-1200A charge amplifier uses the sensitivity (argument part and multiplier part) of the acceleration detector and the range
You can set the output sensitivity. Pressing the [SENS/RNG] key on the CH-1200A will allow you to access the following two settings.
The mode will switch.
- Sensitivity setting mode. The pC/EU indicator on the mode display will light up.
- Range (output sensitivity) setting mode. The mV/EU indicator lights up on the mode display.
In sensitivity setting mode, the sensitivity of the charge output type accelerometer connected to the CH-1200A is determined.
Set the (pC/(m/s²)) value. The argument part can be set to a value between 1.00 and 9.99, and the multiplier part can be set to a value between 0.01, 0.10, 1.00, 10.0, and 100. Set the argument part and multiplier part separately according to the sensitivity of the accelerometer.
In Range (Output Sensitivity) setting mode, you set the range (output sensitivity) of the signal output from the CH-1200A. When inputting the output of the CH-1200A to an analysis device, set the unit calibration (EU) function of the analysis device to a value corresponding to the range (output sensitivity). The sensitivity of the acceleration detector itself is irrelevant.
Table 1 shows the range (output sensitivity, etc.) that can be set on our CH-1200A charge amplifier.
The selectable range (output sensitivity) depends on the multiplier value of the set accelerometer sensitivity.
It will be restricted.
The CH-1200A has a maximum output voltage of ±10 V, so the maximum measurable acceleration is determined by the range (output sensitivity). In the 1.00 mV/(m/s²) range, 1 mV is output at 1 m/s², so 10 V is output at 10,000 m/s², and the maximum measurable acceleration is 10,000 m/s². Our previous models, the CH-1200 and CH-1100, had a maximum output voltage of ±5 V, so their maximum measurable acceleration was half the value shown in Table 1.
During the unit calibration of the analysis device, you set the unit name and EU value, etc. The unit name is m/s², and the EU type is V/EU. If the range (output sensitivity) is 1.00 mV/(m/s²), set 0.00100 (mV converted to V) as the EU value.
Table 1. Range (output sensitivity) of charge amplifier CH-1200A and unit calibration settings of the analysis device.
| Charge amplifier range (output sensitivity) | Unit calibration settings for the analysis device | ||||
| Range display | Output sensitivity | Maximum measured acceleration | Unit name | EU value | EU type |
| 0.01 | 0.0100 mV/(m/s2) | 1,000,000 m/s2 | m/s2 | 0.0000100 | V/EU |
| 0.03 | 0.0316 mV/(m/s2) | 316,000 m/s2 | m/s2 | 0.0000316 | V/EU |
| 0.10 | 0.100 mV/(m/s2) | 100,000 m/s2 | m/s2 | 0.000100 | V/EU |
| 0.31 | 0.316 mV/(m/s2) | 31,600 m/s2 | m/s2 | 0.000316 | V/EU |
| 1.00 | 1.00 mV/(m/s2) | 10,000 m/s2 | m/s2 | 0.00100 | V/EU |
| 3.16 | 3.16 mV/(m/s2) | 3,160 m/s2 | m/s2 | 0.00316 | V/EU |
| 10.0 | 10.0 mV/(m/s2) | 1,000 m/s2 | m/s2 | 0.0100 | V/EU |
| 31.6 | 31.6 mV/(m/s2) | 316 m/s2 | m/s2 | 0.0316 | V/EU |
| 100 | 100 mV/(m/s2) | 100 m/s2 | m/s2 | 0.100 | V/EU |
| 316 | 316 mV/(m/s2) | 31.6 m/s2 | m/s2 | 0.316 | V/EU |
| 999 | 1000 mV/(m/s2) | 10 m/s2 | m/s2 | 1 | V/EU |
Furthermore, the accelerometer has a maximum measurement input that is determined according to the range (output sensitivity) of the charge amplifier.
If vibrations exceeding the speed are applied, the OVER lamp on the charge amplifier will light up, and the charge amplifier will...
The pump output will saturate. Once the output saturates, it will take several seconds to recover. Before taking a measurement or...
To prevent the OVER lamp from lighting up during measurement, adjust the charge amplifier's range (output sensitivity).
Please set it.
Regarding the type of acceleration sensor and the sensitivity setting of the charge amplifier.
Table 2 shows our charge-output type accelerometers and the settings for the CH-1200A charge amplifier used with them. The charge sensitivity values for the charge-output type accelerometers shown in Table 2 are typical values.
Charge sensitivity varies from detector to detector, so please set the sensitivity value indicated in the shipping characteristics sheet or test report included with the detector.
The CH-1200A charge amplifier has an input-referred noise level of 0.05 pC (rms) or less. The input-referred noise level converted to acceleration values is shown in Table 2.
Table 2 Sensitivity settings for charge output type accelerometer and charge amplifier CH-1200A
| Charge output type accelerometer | Charge amplifier | |||||
| Model name | Features | Charge sensitivity (typ.) |
maximum usage acceleration |
sensitivity (Argument section) |
sensitivity (Multiplier part) |
Input conversion noise (rms) |
| NP-2106 | Ultra-compact and lightweight | 0.035 pC/(m/s2) | 100,000 m/s2 | 3.50 | 0.01 | 1.43 m/s2 |
| NP-2110 | Small and lightweight | 0.16 pC/(m/s2) | 10,000 m/s2 | 1.6 | 0.10 | 0.31 m/s2 |
| NP-2710 | Small size/high temperature | 0.306 pC/(m/s2) | 22,600 m/s2 | 3.06 | 0.10 | 0.16 m/s2 |
| NP-2910 | Small and general-purpose | 0.3 pC/(m/s2) | 50,000 m/s2 | 3.00 | 0.10 | 0.17 m/s2 |
| NP-2810 | small size | 1.2 pC/(m/s2) | 20,000 m/s2 | 1.20 | 1.00 | 0.042 m/s2 |
| NP-2120 | General purpose | 5 pC/(m/s2) | 8000 m/s2 | 5.00 | 1.00 | 0.010 m/s2 |
| NP-2560 | Lightweight 3-axis | 0.04 pC/(m/s2) | 25,000 m/s2 | 4.00 | 0.01 | 1.25 m/s2 |
summary
When directly connecting an accelerometer to an analysis device such as an FFT analyzer or data station, the sensitivity of the accelerometer is directly set in the unit calibration function of the analysis device.
When connecting a charge output type accelerometer to a charge amplifier and inputting the output of the charge amplifier to an analysis device, if a typical charge amplifier is used, the sensitivity of the accelerometer should be set to the charge amplifier.
This setting will be configured. No settings will be configured on the analysis device side.
The value to set in the unit calibration function of the analysis device is the range (output sensitivity) of the charge amplifier.
Check what range (output sensitivity) the amplifier is set to, and determine how many volts (mV) the charge amplifier is designed to output when an acceleration of 1 m/s² is detected within that range. Then, set the unit calibration function of the analysis device according to that value.
If the magnitude of the acceleration generated changes due to a change in the object being measured or the measurement conditions, and the range (output sensitivity) of the charge amplifier is changed, then the unit calibration settings on the analysis device must also be changed.
The maximum usable acceleration of the accelerometer and the range (output sensitivity) of the charge amplifier are determined accordingly.
It is not possible to measure vibrations exceeding the maximum measured acceleration. Select an acceleration detector and set the range (output sensitivity) of the charge amplifier to match the maximum magnitude of the vibration that actually occurs. If the charge amplifier overloads during the installation/removal of the acceleration detector or during preparation for measurement, either wait until the charge amplifier output stabilizes before taking the measurement, or take measures to prevent large vibrations from being applied during installation/removal/preparation.
(Excerpt from the email newsletter issued on April 17, 2019)
