"In practical application, the application of RFID system should comprehensively consider many factors affecting the system performance, such as location, distance, temperature, humidity, interference and so on. For the untested RFID system, the overall performance of the system is not clear, which may affect the actual application effect and even attack the end user's confidence in RFID technology itself.
Different wireless signal propagation methods need different test equipment support, and different methods should be adopted. ISO / IEC 18047-3 defines the test method for the performance characteristics of RFID tags used for article management, and specifies the general requirements and test requirements for tag performance. The specific test contents are analyzed below.
Functional test of induction label conforming to ISO / iec18000-2, ISO / IEC 18000-3 and ISO / IEC18000-6. This part specifies the test contents and test methods of induction label, including identification magnetic field strength threshold, read magnetic field strength threshold, write magnetic field strength threshold, working magnetic field strength, generated magnetic field strength and load modulation.
For different test contents, the test methods are similar: first set the test working frequency, then set the amplitude of the waveform generator, then put the label into the test device, send specific instructions, and gradually increase the amplitude until the label responds. Then carry out targeted measurement according to different test contents, record test results and calculate the value of test contents. Taking the identification magnetic field strength threshold test as an example, the flow chart is shown in Figure 1, where urhta is the amplitude of the current waveform generator.
Figure 1: identification magnetic field strength threshold test process for 18000-2 label
The differences of test processes under different protocols are mainly reflected in the changes of various parameters and instructions in the test process, specifically:
Test frequency
In the inductive label test, the corresponding frequency in the label test conforming to ISO / iec18000-2 protocol is 125kHz or 134.2khz; The corresponding frequency in the label test in accordance with ISO / IEC 18000-3 protocol is 13.56MHz; In the label test in accordance with ISO / IEC18000-6 protocol, the corresponding frequency points are one step per 5MHz from 860MHz to 960MHz, and three additional frequency points are 866mhz, 915MHz and 953mhz.
Test initial amplitude
In the test of identifying magnetic field strength threshold, reading magnetic field strength threshold and writing magnetic field strength threshold, the initial amplitude of the signal generator is set below the identifying magnetic field strength threshold (generally 0); In the tests of working magnetic field strength, living magnetic field strength and load modulation, the initial amplitude is set as the threshold of identifying magnetic field strength.
Test instruction
Use "inventory instruction" in the test of identifying magnetic field strength threshold, working magnetic field strength, survival magnetic field strength and load modulation; In the test of read magnetic field strength threshold and write magnetic field strength threshold, use "read instruction" and "write instruction" respectively. In addition, the "query command" can also be used in the working magnetic field strength test.
Test result value
In the test of identifying magnetic field strength threshold, reading magnetic field strength threshold and writing magnetic field strength threshold, the value of the test result is the value in all test records; In the working magnetic field strength, survival magnetic field strength and load modulation test, the value of the test result is the value in all test records.
Test process
The test processes of different protocols on the same test content are the same, while the test processes of different test contents are generally similar, but the specific steps are slightly different. For example, in the test of read magnetic field strength threshold and write magnetic field strength threshold, the test needs to start from one storage block until the end of one storage block; In the test of working magnetic field strength and living magnetic field strength, the working magnetic field strength test needs to send instructions first, and then adjust the waveform amplitude value, while in the living magnetic field strength test, the waveform amplitude value is adjusted first, and then send instructions.
Function test of electromagnetic propagation label
This part specifies the test contents and methods of electromagnetic propagation labels, including identifying electromagnetic field strength threshold and frequency peak, reading electromagnetic field strength threshold, writing electromagnetic field strength threshold, sensitivity degradation, working electromagnetic field strength, survival electromagnetic field strength, radar cross section change rate, interference suppression, identification change rate and writing change rate.
For all test contents, test all frequency points with step of 5MHz in the frequency band of 860MHz ~ 960MHz, as well as the three frequencies of 866mhz, 915MHz and 953mhz specified in ISO / IEC 18047-6. For different test contents, the test method is very similar to the test process of the above induction label. The test process differences of different test contents mainly lie in the changes of various parameters and instructions in the test process, specifically:
Test initial amplitude
In the identification electromagnetic field strength threshold and peak value, read electromagnetic field strength threshold, write electromagnetic field strength threshold and sensitivity degradation test, the initial amplitude of the signal generator is set below the identification magnetic field strength threshold (generally 0); In the test of working electromagnetic field intensity, survival electromagnetic field intensity and radar cross section change rate, the initial amplitude of the signal generator is set as the threshold of identifying electromagnetic field intensity; In the continuous wave interference suppression test, the amplitude of the signal generator is set as the recognition electromagnetic field intensity threshold, the initial amplitude of the interference generator is set below the recognition electromagnetic field intensity threshold (generally 0), while in the modulation signal interference suppression test, the amplitude of the signal generator is set as 6dB higher than the recognition electromagnetic field intensity threshold, The initial amplitude of the interference generator is set to be lower than the recognized electromagnetic field intensity threshold (generally 0); In the identification change rate and write change rate tests, the initial amplitude of the signal generator is set to be 3dB higher than the identification electromagnetic field intensity threshold (9dB higher than the identification electromagnetic field intensity threshold).
Test instruction
Specific instructions are not specified in sensitivity degradation, working electromagnetic field strength, survival electromagnetic field strength, radar cross section change rate, identification change rate and write change rate tests; Identify electromagnetic field intensity threshold, peak value, read electromagnetic field intensity threshold and write electromagnetic field intensity threshold. Inventory instruction, read instruction and write instruction are used respectively in the test; In the interference suppression test, specific instructions shall be specified in the continuous wave interference suppression test and modulation signal interference suppression test, and the continuous wave shall also be sent in the continuous wave interference suppression test.
Test result value
In the identification electromagnetic field intensity threshold, reading electromagnetic field intensity threshold, writing electromagnetic field intensity threshold and sensitivity degradation test, the value of the test result is the value of all test records; In the test of working electromagnetic field intensity, survival electromagnetic field intensity, radar cross section change rate, interference suppression, identification change rate and write change rate, the value of the test result is the value in all test records.
Test process
The test processes of different test contents are generally similar, but the specific steps are slightly different. For example, in the test of read electromagnetic field intensity threshold and write electromagnetic field intensity threshold, the test needs to start from one storage block until the end of one storage block; In the sensitivity degradation test, it is necessary to measure each angle in the horizontal and vertical directions; In the interference suppression test, in the continuous wave interference suppression test, the test is stopped until the tag cannot respond to the modulation signal command, and in the modulation signal test, the test is stopped until the tag responds to 50% of the expected generator command at the specified amplitude level.
Function test of 433.920mhz electromagnetic propagation label conforming to ISO / iec18000-7 protocol
This part specifies the functional test contents and test methods of 433.920mhz electromagnetic propagation label in accordance with ISO / iec18000-7, including: identifying electromagnetic field strength threshold and frequency tolerance, reading electromagnetic field strength threshold and frequency tolerance, writing electromagnetic field strength threshold, sensitivity directionality, interference suppression, working electromagnetic field strength and survival electromagnetic field strength.
Compared with the above type of label performance test, the test setting of 433.920mhz electromagnetic propagation label conforming to ISO / iec18000-7 protocol is more complex: the test equipment shall be placed in anechoic chamber or other completely specific position, which shall not be affected by interference source and transmission (such as specific signal reflection, absorption or blockage). The center frequency used in the test is 433.920mhz, and 50KHz FSK modulation is carried out. The waveform and timing are defined in ISO / IEC 18000-7. The signal source output must be adjustable within 100dB in 10dB steps, and the output must be at least 10dBm. The modulation of the signal uses the code generator to generate the corresponding correct command and timing. In the test, FSK receiver and decoder are used to receive, decode and send the tag response to the corresponding monitoring software, so that the tag response can be evaluated.
For different test contents, the test process is: first, set all test equipment positions, configure signal sources, install labels, send corresponding instructions, adjust the signal sources until the test labels send a reliable response, then carry out targeted measurement according to different test contents, record test results and calculate the value of test contents. Taking the identification electromagnetic field intensity threshold test as an example, the flow chart is shown in Figure 2.
Figure 2: identification of electromagnetic field strength test process
The differences between tests of different test contents mainly lie in the changes of various parameters and instructions in the test process, specifically:
Test frequency
433.900mhz, 433.920mhz and 433.940mhz need to be tested in the test of identifying electromagnetic field intensity threshold and frequency tolerance, reading electromagnetic field intensity threshold and frequency tolerance, and writing electromagnetic field intensity threshold; Only 433.920mhz needs to be tested in the test of sensitivity directivity, working electromagnetic field strength and living electromagnetic field strength; In interference suppression, it is necessary to test the interference frequencies of 433.920mhz, 434.170mhz, 433.670mhz, 434.420mhz and 433.420mhz.
Test distance
In the test of identifying electromagnetic field strength threshold and frequency tolerance, reading electromagnetic field strength threshold and frequency tolerance, writing electromagnetic field strength threshold, sensitivity directivity and interference suppression, the test distance from the recommended label position to the reference antenna is 2m, and 3M is better. In the test of working electromagnetic field strength and living electromagnetic field strength, the test distance from the recommended label position to the reference antenna is 2m, and 1m is better.
Test instruction
In the test of writing electromagnetic field strength threshold and frequency tolerance, first send the wakeup header command, and then send the write command; In other test items, the wakeup header command is sent first, followed by the collect command.
Test result value
In the test of identifying electromagnetic field intensity threshold and frequency tolerance, reading electromagnetic field intensity threshold and frequency tolerance, writing electromagnetic field intensity threshold and sensitivity directivity, the test results take the values of all measured values; In the test of interference suppression, working electromagnetic field strength and survival electromagnetic field strength, the test results shall be taken from all measured values.
Test process
The test processes of different test contents are generally similar, but the specific steps are slightly different. For example, in the sensitivity directivity test, the label needs to be rotated in 15 ° steps, and the horizontal directions are tested at 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330 and 345 Degrees respectively, The vertical directions are measured on 0, 15, 30, 45, 60, 75 and 90 respectively; In the interference suppression test, the signal source strength is set to be 3dB higher than ethr read, and the signal strength of the interference signal source is set to be 20dB lower than ethr read, then adjust the interference signal source in 3dB steps, test the channel interference suppression irection value of the tag, and repeat the test on the adjacent channel (250kHz) and the second adjacent channel (500KHz); In the working electromagnetic field strength test, a power amplifier needs to be added between the signal source and the antenna; In the survival electromagnetic field strength test, first adjust the power of the signal generator to be higher than Emax, then return to between ethr identification and Emax, and try to read the label.
In practical application, the application of RFID system should comprehensively consider many factors affecting the system performance, such as location, distance, temperature, humidity, interference and so on. For the untested RFID system, the overall performance of the system is not clear, which may affect the actual application effect and even attack the end user's confidence in RFID technology itself. Therefore, before investing and implementing RFID solutions, it is very necessary to carry out certain tests and simulation tests according to the test methods and processes. ISO / IEC 18046-3 is a RFID tag performance test method, which is conducive to tag selection and system design, and promote the better implementation of RFID system.
Source: viku electronic market network“
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