Charge Amplifier XY8102A

Charge Amplifier XY8102A

Ⅰ. OVERVIEW

XY8102A charge amplifier is a kind of low noise charge amplifier whose output voltage is proportional to the input charge, which can be connected with piezoelectric accelerometers and other piezoelectric sensors to measure mechanical quantities such as vibration, shock, dynamic force, etc. It is widely used in the departments of machinery, power, mining, transportation, construction, water conservancy, aviation, aerospace, weaponry, and chemical explosives, etc. Due to its high accuracy, it is also suitable for calibration of accelerometer. Due to high precision, it is also suitable for accelerometer calibration.

XY8102A charge amplifier has the following characteristics:

- Low noise less than 5μv.

- Three decimal sensor sensitivity adjustment, with different sensitivity sensors can be obtained normalized output.

- Wide range of adjustable high and low pass filters and overload indication device.

- Less than 3° phase error between multiple units.

- Maximum output up to 100mA to drive various oscillators of light recording oscilloscopes.

Ⅱ.Technical parameters

2.1 Number of Channels: Single Channel/Unit

2.2 Input Range: Charge: ± 106pC

2.3 Sensitivity: 0.01~1000 mV/pC (-40~+60dB for source capacitance 1nF)

2.4 Sensor sensitivity adjustment: three-digit digital adjustment sensor charge sensitivity 1-1099Pc/Unit (1)

2.5 Accuracy

0.1mV/Unit, 1mV/Unit, 10mV/Unit, 100mV/Unit, 1000mV/Unit five grades, when the equivalent capacitance of the input cable were less than 10nF, 68nF, 22nF, 6.8nF, 2.2nF, respectively, 1kHz reference conditions (2) is less than ± 1%, rated operating conditions (3) is less than ± 2%.

2.6 Filters and Frequency Response:

2.6.1 High-pass filter: lower limit frequency 0.3, 1, 3, 10, 30, 100Hz 6 steps.

Allowable deviation: 0.3Hz,-3dB±1.5dB;1,3,10,30,100Hz-3dB±1dB

Attenuation slope: -6dB/cot

2.6.2 Low-pass filter: upper limit frequency 300, 1k, 3k, 10k, 30k, 100kHz 6 steps.

Allowable deviation: -3dB±1dB

Attenuation slope: -12dB±2dB/oct

2.7 Output Characteristics

2.7.1 Maximum output amplitude: ±10Vp

2.7.2 Maximum output current: ±100mA

2.7.3 Minimum load resistance: 100Ω

2.7.4 Harmonic distortion: <1% at frequency below 30kHz, capacitive load <47nF full-amplitude output

2.8 Output noise: ≤ 5×10 -3pC (maximum gain, converted to the input)

2.9 Overload indication: When the output is greater than |10±1Vp|, the overload indicator will light up.

2.10 Operating Temperature: -10~50°C

2.11 Power supply: AC110/220V±10% 0.2A or DC±18∽28V 200mA

2.12 Dimensions: 70 (W) × 132.5 (H) × 200 (D) m

2.13 Weight: about 1.5 Kg

Note: 

(1) Unit: refers to the mechanical quantity unit corresponding to the sensor sensitivity unit, such as gravity acceleration unit g, acceleration unit mSˉ ², force unit N, etc.

(2) Reference conditions:

a, 20℃±2℃

b, relative humidity (45-75)%RH

c, AC220V ± 2% or DC ± 19-21V

d, load resistance > 10kΩ

(3) Rated operating conditions:

a, 0℃-40℃

b, relative humidity (20-90)%RH

c, supply voltage AC110/220V±10% or DC±18-28V

d, load resistance>100Ω

Ⅲ.Principle of operation

XY8102A charge amplifier by the charge amplifier stage, preamplifier normalized voltage amplifier stage, high and low-pass filter, output amplifier stage, overload indication and regulator power supply five parts. The working principle of each part is briefly described as follows:

3.1 Charge stage

The charge amplifier uses a high input impedance operational amplifier as the input stage. A capacitor in the feedback loop of the amplifier forms an integrating network that integrates the input current. This input current is formed by the charge generated on the high impedance piezoelectric element inside the accelerometer. The function of the amplifier is to counterbalance this current so that an output voltage proportional to the charge is formed. Figure 1 represents the equivalent circuit of a piezoelectric accelerometer connected to a preamplifier.

Fig. 1 Working principle of charge amplifier

Cc: Cable capacitance

Rp: Preamplifier input resistance value

Cp: Preamplifier input capacitance

Rf: Feedback resistance

Cf: Feedback capacitance

-A: operational amplifier gain, negative sign indicates inversion

Vo: amplifier output voltage

In general, the resistance of the accelerometer, the preamplifier input resistance, and the feedback loop resistance are high, so Figure 1 can be simplified as shown in Figure 2:

Ct: Ca+Cc+Cp

I: Total current outflow from acceleration

Ii: current out of Ct

Ic: Current in the feedback loop of the operational amplifier.

The input voltage Vi and output voltage Vo are related by the following equation

Vo=-AVi

Vc=Vo-Vi=Vo-Vo/-A=(1+1/A)×Vo

Applying Kirchhoff's law in Fig. 2 then:

I+Ic+Ii=0

The current is related to the charge generated by the piezoelectric element and the voltage across the capacitor its current expression is:

I=dQa/dt

Ic=Cf×dVc/dt=(1+1/A)×Cf×dVo/dt

Ii=Ct×dVi/dt=1/A×Ct×dVo/dt

The current flowing from the accelerometer according to Kirchhoff's equation can be given as

dQo/dt=-(1+1/A)×Cf×dVo/dt-1/A×Ct×dVo/dt

Integrating the above equation yields:

Considering the large value of A (≥105 ) then the above equation can be simplified as

Vo=-Qa/Cf

From the above equation, it can be clearly seen that the output voltage is proportional to the input charge, and the sensor capacitance and cable capacitance have almost no effect on the output voltage of the amplifier, which means that the charge amplifier can be used with longer input cables without affecting its sensitivity, which is an important feature of the charge amplifier. This amplifier switches different feedback capacitance to get ±20dB dynamic range.

3.2 Normalized Voltage Amplifier Stage

Normalization is obtained by using an operational amplifier with adjustable gain so that it has different gains for sensors with different sensitivities.

It is known that an operational amplifier is shown in (Fig. 3) and its closed-loop gain can be determined by the following equation:

 -A=Zf/Zi

From the above equation, it can be seen that to change the gain, it is only necessary to change Zf or Zi. This instrument Zf is fixed 10kΩ and Zi by three sets of decimal precision metal film resistors 2 R1-9, 2R10-18, 2 R19-27 composition, when the instrument panel sensor sensitivity dial to 1-0-0, Zi = 1kΩ

Gain-A=10kΩ/1kΩ=10, and when dialed to 10-0-0, Zi=1kΩ×9+1kΩ=10kΩ, gain-A=10kΩ/10kΩ=1

Set the sensitivity of the acceleration sensor for 40pC / g, and give 10 g vibration, if the charge amplification stage output voltage of 0.4V sent to the normalization amplification stage, at this time if the sensor sensitivity dial to 4-0-0, then Zi = 4kΩ, the gain - A = 10kΩ/4kΩ = 2.5, so that the amplified output voltage by this stage becomes 0.4V × 2.5 = 1V, that is, the instruction Instrumentation on the 1V that is 10g, so as to achieve the purpose of "normalization".

3.3 Filter

The instrument has built-in adjustable high-pass filter and low-pass filter. The instrument's high-pass filter is a single-stage RC filter immediately after the output of the charge amplifier stage, which is attenuated by 6 dB per octave. 6 different lower limit frequencies are obtained by changing R. However, in the 0.3 Hz stage, the lower limit frequency is set at 10g. However, at 0.3 Hz, the actual high-pass filter frequency is about 0.08 Hz, while the lowest lower frequency of the instrument is determined by the charge amplifier stage. The low-pass filter in the back stage is a second-order Butterworth-type RC active filter, resulting in good flatness in the passband.

3.4 Output Amplifier

The output amplifier of this instrument is a large current output operational amplifier, which makes the output current up to 100mA and can work stably under certain capacitive load.

3.5 Overload Indicator

Overload indicator circuit consists of two groups of symmetrical trigger, a group for positive signals, a group for negative signals, the size of 10μS pulse can make the circuit action and delay 2 seconds, the input signal from the normalizing amplifier and the output amplifier were led out of the two places, so that when any one of the output voltage > 10V р, can be made to overload indicator action, the indicator for the red light-emitting diode.

3.6 Voltage regulator

Instrument ± 15V regulated power supply for a typical integrated regulated power supply, transformer step-down, rectifier, filtering, voltage regulator.

Ⅳ.Panel Functions

4.1 Overload indication

Indicates whether the instrument output peak value exceeds 10V;

4.2 Lower Limit Frequency

Correct selection of the lower limit frequency (high-pass filter) can suppress low-frequency interference signals and improve the signal-to-noise ratio. The lower limit frequency should be placed below 0.1 times the lowest frequency of the measured signal, the measurement should pay attention to the pyroelectric effect of the sensor, mating general piezoelectric acceleration sensor, the lower limit frequency should not be too low, if you want to measure the low-frequency vibration, it is advisable to use quartz sensors and other temperature effect of the sensor is small, which is particularly important in the low mechanical quantity.

4.3 Charge input

Connect the charge signal output from the sensor. Never connect a voltage signal from the charge input.

4.4 Decimal point

A lit left decimal point indicates a sensor sensitivity range of 1-10.99 Pc/Unit, a lit center decimal point indicates a sensor sensitivity range of 10.0-109.9 Pc/Unit, and a lit right decimal point indicates a sensor sensitivity range of 100-1099 Pc/Unit.

4.5 Sensor Sensitivity Adjustment

For adjusting the sensitivity of the sensor connected to it.

4.6 Sensor sensitivity range toggle switch

When the sensor sensitivity in 1-11 Pc / Unit, the switch is placed in the upper position, the left decimal light, according to the "output mV / Unit" knob above the indication of the reading; when the sensor sensitivity in the 10-110 Pc / Unit, the switch is placed in the middle position, the middle decimal light, "output mV / Unit" knob above the indication of the reading to be multiplied by 10, when the sensor sensitivity in the 100-1100 Pc / Unit, the switch is placed in the middle position, the middle decimal light, "output mV / Unit" knob above the indication of the reading to be multiplied by 10, when the sensor When the sensitivity of the sensor is 100-1100 Pc/Unit, the switch is placed in the lower position, the right decimal is illuminated, and the indicated reading above the "Output mV/Unit" knob is multiplied by 100.

4.7 Output mV/Unit

The relationship between sensor sensitivity and output mV/Unit is shown in Table 4.1.

The rest of the analogous

Measured Mechanical Quantity Unit = Output Voltage (mV) /《Actual Output ×××mV/unit》 class

4.8 Upper frequency

Correct selection of the upper limit frequency (low-pass filter), can suppress the sensor self-oscillation peaks and other high-frequency interference, improve the signal-to-noise ratio, the upper limit frequency should be placed in the measured signal in the highest frequency of more than 3 times.

4.9 Voltage input

XY8102A overhaul, calibration, the signal generator output voltage can be accessed from this.

4.10 AC power switch

Controls whether the AC power supply is connected or not. Note that this switch does not work when DC power is supplied.

4.11 110/220V changeover switch

When the switch is placed on the top, it is AC220V input, and placed on the bottom, it is AC110V input.

4.12 Outputs

Instrument signal outputs for connection to voltmeters, oscilloscopes, recorders and other instruments.

4.13 DC Power Input

DC power input. The red wire of the DC power plug connects to the positive side of the power supply, and the blue wire connects to the negative side of the power supply. The yellow wire is connected to zero. The DC plug should be removed at the end of the test to cut off the power supply.

4.14 Fuse Holder

A 0.2A fuse tube is installed inside. When replacing the fuse tube, the amplifier should be disconnected from the power supply. Self-soldered fuses and shorted fuse holders should not be used.

4.15 AC Power Input

AC power input: connect 220V±10%, 50Hz or 110V10%, 60Hz AC power.

V.Methods of use

5.1 Measurement Preparation

A vibration test system consisting of piezoelectric accelerometers and charge amplifiers should be prepared for vibration measurements as follows.

5.1.1 Carefully determine where the transducer is to be mounted and the effect of its possible mass loading. For measurements on panels, small, lightweight accelerometers are required, as any "extra" loading may alter the original motion of the structure, thus invalidating the measurement. 

5.1.2 Estimate the type and magnitude of vibration (periodic, random, shock, etc.) present at the point of sensor installation.

5.1.3 Select the most suitable sensor by considering the above 2 items and environmental factors (temperature, humidity, electromagnetic field).

5.1.4 Examine and calibrate the accelerometer. 

5.1.5 Determine which measurement (accelerometer, combined measurement of velocity or displacement, waveform recording, frequency analysis) is most appropriate for the problem under study.

5.1.6 Select the most appropriate instrumentation by considering frequency and phase characteristics, dynamic range and method of operation.

5.1.7 Draw a sketch of the measurement system, labeling the model and serial numbers of the instruments used.

5.1.8 Select the most suitable mounting method for the transducer by considering the place of use, frequency range, electrical insulation problems and grounding circuit, and the following are a few commonly used mounting methods.

The first direct mounting with screws, which is the best way to solve the frequency response, which is basically in line with the actual standard curve of the accelerometer, if the mounting surface is not very smooth, it is best to apply a layer of silicone grease on the surface in order to increase the mounting stiffness. Sensor mounting screws are not completely screwed in to prevent causing the base surface curvature, affecting the sensitivity of the sensor.

The second when the sensor and the vibration body needs to be electrically insulated between the available insulating bolts and thin mica washers, due to the hardness of the mica, the frequency response is good, but to make the washers as thin as possible.

The third is to move the measuring point with a magnetic screw, it is also insulated, the method is not applicable to the acceleration amplitude of more than 100g occasions.

The fourth uses a gluing technique.

The fifth uses replaceable round or pointed probes, which are convenient for troubleshooting large rotating machinery, but cannot be used in the frequency range above 1000 Hz, where the natural resonant frequency is low.

5.1.9 If used within a liquid or in a very humid environment, the cable and sensor joints must be sealed, 703 silicone rubber is a good sealing material with excellent performance over a wide temperature range of -60°C to +150°C.

5.2 Installation

5.2.1 The charge amplifier can be used in a wide temperature range from -10℃ to +50℃, and the supply voltage is 220V50Hz or 110V60Hz.

5.2.2 Sensor Matching

The instrument can be connected with charge output type accelerometers or force sensors.

5.2.3 Cable selection

The input cable should be low noise cable (provided by the company), the plug and socket of the cable should be screwed tightly, and the cable should be fixed as far away as possible from strong electromagnetic fields, such as transformers, motors, high-power wires and so on. Output cable for ordinary coaxial cable, due to the existence of cable capacitance, to a certain extent, will affect the frequency characteristics of the instrument, especially lengthening the cable, which makes more than 30kHz signal attenuation so as far as possible in the measurement to avoid excessive length of the cable.

5.2.4 Connection of output instruments

Charge amplifier is a secondary instrument, still need to be connected to the three instruments, in order to be measured physical quantities for display, recording, analysis, etc., the output of this instrument is 10Vp/10mA, the output impedance is less than 2Ω, which can satisfy most of the three instruments of the input characteristics. The grounding of the system is automatically completed through the coaxial cable.

5.2.5 Grounding

To prevent industrial frequency interference. The grounding of the measurement system must be taken very seriously.

5.3 Operation

5.3.1 Connect the AC 220V and turn on the power switch to warm up for about 30 minutes.

5.3.2 Connect the output to appropriate indicating and recording instruments-voltmeter, oscilloscope, recorder, frequency analyzer, etc.

5.3.3 Fit the transducer to the object under test, connect the low-noise cable to the transducer, shorting the L5 plug to the core with a metal conductor to release the accumulated charge before connecting to the instrument input socket.

5.3.4 Set the sensor sensitivity to match that of the connected sensor.

5.3.5 Select the appropriate "Output mV/Unit" gear, so that the signal output is less than 10V and more than 3V, in order to get the best signal-to-noise ratio, if it is not possible to determine, it should be placed in the lower sensitivity position first.

5.3.6 Select reasonable upper and lower limit frequencies.

5.3.7 Carry out the measurement

5.3.8 Turn off the power when finished

5.3.9 Application example

Measurement of an object vibrating with a charge sensitivity of 12.5 pC/ms-2 accelerometer with a vibration frequency of about 30 Hz.

The sensor sensitivity range switch is placed in the middle position, the sensor sensitivity code is adjusted to 12.5 Pc / Unit, the lower frequency limit is placed at 0.3Hz, the upper frequency limit is placed at 0.3kHz. adjust the output mV / Unit from low to high to 100mV / Unit file, (because the sensor sensitivity of 12.5pC/ms-2 in the 10.0-109.9 Pc / Unit range, this time the incremental gain is about 0.0 to 0.5mV / Unit, and the output mV / Unit is about 0.5 to 0.5mV / Unit. Unit range, the gain reading should be output mV/Unit * 10 that is, 1000mV/Unit), the overload lamp does not light up, the output is connected to a voltmeter, the reading is 3.5Vp. Then the measured object vibration amount is

5.4 Precautions

5.4.1 Interference with 50Hz 

When the instrument is in use, if there is industrial frequency interference, it can be checked from the following aspects.

a. Insulate the sensor from the mechanism where it is installed.

b, poor contact of input cable plug, shielding layer does not work, screw the plug tightly.                     

c、Move the grounding point to the analyzing or reading out equipment.

5.4.2 "background noise" judgment

In the test if the noise is large and can not distinguish between the test problem or system problems, check the vibration measurement system "background noise" level is necessary. Leave the sensor from the measurement point, installed in a non-vibrating body, such as placed in the corner, and measure the device's "apparent" vibration level, then the amplifier output is quiet and no obvious noise, which is the system's normal "background noise". This is the normal "background noise" of the system. This is the way to judge whether the system (amplifier) is normal or not. In actual vibration measurements, in order to obtain the appropriate accuracy, the "apparent" level should be less than one-third of the measured vibration.

VI. Maintenance

6.1 The charge amplifier belongs to high input impedance instruments, all parts of the input chain should be kept clean, once contaminated, a clean silk cloth can be used with a little anhydrous ethanol to clean and dry. When the instrument is out of service, the dust cap of the input socket should be screwed on.

6.2 Do not connect the voltage signal directly to the PE input of the instrument. For performance checking, the voltage signal can be input from the V input.

6.3 In principle, this instrument is laboratory equipment, and should be used in other occasions to avoid acid, alkali, salt spray, rain and too strong radiation field.

6.4 Within one year after the instrument is shipped out of the factory, the company is responsible for repairing or replacing it free of charge if it fails due to non-man-made factors.

Yangzhou Xiyuan Electronic Technology Co.,Ltd.

Building 2,217 kaifa west road,high-tech development zone, yangzhou, jiangsu,China 225128

Mobie Phone: +86 180-5105-8377

Tel: +86 514-82885589

Whatsapp:+86 182-6066-6867

Email: sale1@yzxyt.com

Fax: +86 514-82885089