The signal conditioning module of the universal testing machine is part of the measurement system The core function of the "signal preprocessing center" is to process the weak and noisy raw electrical signals output by sensors into stable, accurate, and standard signals that meet data acquisition requirements, laying the foundation for subsequent analog-to-digital conversion (A/D conversion) and data processing. Its functions are designed around the four core objectives of "signal amplification, noise suppression, error compensation, and signal adaptation". The following is a specific functional analysis (combined with equipment practical scenarios and technical details):

1、 Core functions1: Weak signal amplification (the most basic core function)

Functional principle:

The output signals of core sensors such as force sensors and extensometers are weak analog signals (usually At the μ V level, such as a 1000N load corresponding to a 100 μ V signal, the A/D converter has extremely low recognition accuracy for weak signals and is susceptible to interference, resulting in data distortion. The signal conditioning module amplifies weak signals to the mV level (usually 1000 to 10000 times) through a programmable amplifier (PGA), improving the signal-to-noise ratio and recognizability of the signal.

Key technical details:

Adjustable magnification factor: supports sensor types (such as force sensors, extensometers) and testing scenarios (small loads)/Manually or automatically adjust the amplification factor (such as 1000 times, 5000 times, 10000 times) for large loads to ensure that signals of different amplitudes can be accurately amplified;

High gain accuracy: amplification factor errorless than or equal to± 0.1%, to avoid measurement errors caused by magnification deviation (such as ± 0.5% for an error of 1000 times magnification, which will directly lead to measurement errors in force values)reachable ±0.5%）；

Low input bias current:≤1nA， Reduce the load impact on the sensor output signal (avoid the sensor signal being "pulled down" or distorted).

Application Scenario:

Small load testing (such asMicro spring tension test below 10N: The sensor output signal is only a few μ V and needs to be amplified by 10000 times to several tens of mV in order to be accurately recognized by the A/D converter;

Strain measurement (such as metal yield strain testing): The output signal of the extensometer is usually≤10μV， High magnification is required to capture microscopic strain changes.

2、 Core functions2: Noise suppression and filtering (improving signal purity)

Functional principle:

There is a large amount of electromagnetic interference (such as high-frequency noise generated by servo motors, power supplies, and frequency converters) and mechanical vibration noise in the testing environment. These noises will be superimposed on the original signal of the sensor, causing the signal to Distortion "(such as jagged fluctuations in the force curve). The signal conditioning module filters out unwanted noise and retains effective signals through filtering circuits and electromagnetic shielding design.

Key technical details:

Multi type filtering modes:

Low pass filter (mainstream): filters high-frequency noise above the set frequency (such as the cutoff frequency)1kHz、5kHz）， Adapt to different testing speeds (choose low cutoff frequency for low-speed testing and high cutoff frequency for high-speed testing);

Power frequency filter（50Hz/60Hz): Specialized in filtering power frequency interference generated by grid voltage (such as 50Hz noise from laboratory 220V grid), it is a common interference source filtering method;

Notch filter: Accurately filters interference at specific frequencies (such as 100Hz noise generated by motor operation) to avoid affecting the signal;

High common mode rejection ratio（CMRR）：≥ 120dB@50Hz Suppress common mode interference (such as ground interference at both ends of sensor cables) to ensure the accuracy of signal differential amplification;

Shielding design: The module shell adopts a metal shielding cover, the cable uses twisted pair shielded wire, and the grounding resistance≤ 4 Ω, further reducing electromagnetic interference.

Application Scenario:

High frequency noise generated by the operation of hydraulic pumps during testing of heavy-duty hydraulic presses（≥1kHz）， It needs to be filtered through a low-pass filter (cut-off frequency 1kHz) to avoid fluctuations in force data;

Precision strain testing: Environmental electromagnetic noise (such as computers and frequency converters) can cause strain signal drift, which requires power frequency filtering+Shielding design to control strain measurement error within ± 1 μ m/m.

3、 Core functions3: Signal error compensation (correcting system deviation)

Functional principle:

The sensor itself has inherent errors such as temperature drift and zero offset. The signal conditioning module corrects these system errors through hardware compensation circuits and software calibration algorithms to ensure signal accuracy.

Key technical details:

Temperature compensation:

Hardware compensation: Built in temperature sensor and compensation resistor, when the ambient temperature changes (such as23 ℃± 5 ℃), automatically adjust the gain or bias voltage of the amplification circuit to offset the temperature drift of the sensor (such as drift ≤ 0.005% FS for every 10 ℃ change in temperature of the force sensor);

Software compensation: By storing calibration coefficients, the corresponding relationship between temperature and error is written into the program, and the measured values are corrected in real time;

Zero point compensation and calibration:

Support manual or automatic zero calibration (such as zero load reset before testing), correct the zero offset of the sensor (such as output when the sensor is unloaded after long-term use)0.1 μ V signal, zeroed through zero point compensation);

Support external standard signal calibration (such as inputting a known standard voltage signal to calibrate the gain accuracy of the amplifier circuit);

Linearity compensation: corrects the nonlinear errors of sensors and amplification circuits (such as the nonlinear relationship between sensor output and actual physical quantities), and controls the linearity error within a segmented calibration algorithm Within ± 0.02% FS.

Application Scenario:

High temperature environment testing (such as testing with high and low temperature environmental chambers): temperature variation range-70 ℃~300 ℃, temperature compensation is required to ensure that the force/displacement signal is not affected by temperature;

Long term continuous testing (such as production lines)24-hour quality inspection): The zero point of the sensor will slowly drift over time, and the deviation needs to be corrected through automatic zero point calibration (reset every 100 tests).

4、 Core functions4: Signal adaptation and conversion (matching subsequent acquisition steps)

Functional principle:

The type and amplitude of the signal output by the sensor (such as differential signal, single ended signal) may varyThe input requirements of the A/D converter do not match, and the signal conditioning module adapts the signal to a standard signal that can be received by the A/D converter through a signal conversion circuit.

Key technical details:

Signal type conversion:

Convert differential signals from sensors (such as differential outputs from strain gauge bridges) into single ended signals (such as ground reference signals), suitable for most applicationsInput requirements for A/D converters;

Support current signal（Conversion between 4-20mA and voltage signal (0-10V) (some external sensors are current output type);

Signal amplitude clamp: limits the amplified signal amplitude toThe input range of the A/D converter (such as ± 10V) should be adjusted to avoid signal overload that may cause damage or data overflow to the A/D converter;

Excitation power supply: Provide stable bridge excitation power supply for strain gauge sensors (force sensors, extensometers) (usually5V or 10V), excitation voltage stability ≤ ± 0.01%/h, ripple ≤ 1mV, ensuring stable sensor operation.

Application Scenario:

External high-precision extensometer (current output type)4-20mA): The current signal needs to be converted into a 0-10V voltage signal through a signal conditioning module, and then input into an A/D converter;

The signal after high magnification (such as20V): Restricted to ± 10V through amplitude clamping function to avoid exceeding the input range of the A/D converter (usually ± 10V).

5、 Core functions5: Multi channel synchronous acquisition control (adapted to multi parameter measurement)

Functional principle:

The universal testing machine needs to synchronously collect signals from multiple channels such as force value, displacement, strain, etc. (such as force value channel, displacement channel, strain channel). The signal conditioning module ensures that the signal acquisition rhythm of all channels is consistent through a synchronous control circuit, achieving timestamp alignment of data.

Key technical details:

Multi channel parallel processing: supportAt least 3 channels (force, displacement, strain) are synchronously collected, and the isolation between channels is ≥ 100dB to avoid signal crosstalk between channels;

Synchronous triggering mechanism: Through hardware triggering (such as test start signal) or software triggering, ensure that all channels start collecting simultaneously and the sampling rate is consistent≤± 1% (e.g. when sampling at 1000Hz, the sampling rate deviation of each channel is ≤ 10Hz);

Data caching and transmission: built-in caching module (capacity)≥1MB）， Temporarily store multi-channel synchronized data collection to avoid data loss due to insufficient transmission speed, and support high-speed transmission to the controller through USB and Ethernet interfaces.

Application Scenario:

stress-Strain curve drawing: It is necessary to synchronously collect force values (calculate stress) and strain data. If the channels are not synchronized, it will cause the inflection point of the curve to shift (such as misjudgment of metal yield point);

Dynamic fatigue testing: It is necessary to synchronously collect force values and displacement signals during the cyclic loading process to ensure accurate data analysis for each cycle.

6、 Performance indicators and selection references for signal conditioning modules

summary

The signal conditioning module of the universal testing machine is connected to the sensor and data acquisition system The core value of "bridge" lies in "purifying signals, correcting errors, and adapting to data acquisition", which directly determines the accuracy and stability of the measurement system. The key functions can be summarized as:

Amplify weak signals to enhance recognizability;

Filter noise interference to ensure signal purity;

Compensate for system errors such as temperature and zero point;

Convert signal type/Amplitude, matched with A/D converter;

Synchronize multi-channel collection to ensure accurate data correlation.

When selecting, it is necessary to consider the accuracy level of the equipment (such asA comprehensive judgment is required for 0.1 level equipment, including the selection of high CMRR and low drift conditioning modules, testing parameters (such as high amplification and low noise for strain testing), and environmental conditions (such as strong temperature compensation for high temperature scenarios). At the same time, the manufacturer is required to provide calibration reports for the modules to ensure that the performance indicators meet the standards. Regularly check the shielding grounding and filtering parameter settings of the module during use to avoid distortion of test data caused by module failures.