Problems needing attention when selecting DAQ prod

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Problems needing attention when selecting data acquisition (DAQ) products


today's data acquisition (DAQ) products should use modern technology and excellent design for measurement work - accurate reading of data. Modern technology and design can provide some specific advantages for the wind pressure deformation performance testing method of building curtain wall gb/t 15227 (9) 4. However, many manufacturers of data acquisition cards still use the technology of the 1980s. Its design limits the accuracy of monitoring results, and the results are often only approximate or estimated values. Since the board produced with outdated technology can only get the measured estimated value, why should manufacturers use it? There are many reasons: unwilling to invest more in DAQ product production, not pursuing innovative technology, and directly using old technology. But for whatever reason, the result will only be an inaccurate measurement. Ni's DAQ products are famous for measurement ready (accurate measurement immediately). It uses a series of technologies and precise designs to ensure high-precision measurement. Even low-cost DAQ products also have measurement ready characteristics. Before purchasing a DAQ card, you should first understand these technologies, understand how important they are to the measurement work, and determine whether the DAQ product you want to buy has these important technical characteristics

technical problems

1 Does this board need calibration

some DAQ boards are designed with self calibration function, which means that they do not carry components that are easy to cause gain and offset errors, such as voltage dividers or amplifiers. Therefore, such DAQ products can use their excellent design for self calibration

2. Can this board be calibrated automatically

measurement ready DAQ boards can be calibrated automatically, so they themselves reduce the possibility of various offset and gain errors. Offset errors are usually caused by environmental changes, such as electric emission, temperature drift, etc; Gain error is often caused by the different bearing capacity of various components. If the board is designed properly, these errors can be eliminated automatically without external help. To calibrate the board automatically, run the driver through the software command. There are two methods of automatic calibration: using on-board coefficient; Accurate on-board voltage and temperature values using reference on-board coefficients

on board coefficient is used for automatic calibration of boards with gain. Usually, the board is calibrated before leaving the factory, and the coefficient is stored in the EEPROM on the board, which reflects the gain and offset errors related to the board. Each time the driver is run through a software command, the program reads these coefficients and uses them to correct the measured readings. When calibrating with this method, the user can also redefine the on-board calibration coefficient by providing a known voltage value

The on-board precision voltage and temperature values of the reference on-board coefficient are used for advanced automatic calibration. The on-board precision voltage value is stored in a channel in digital form, and then the measured value is compared with it to obtain the offset coefficient; Change the precision reference value to a new and larger value to define the gain error value. Considering the change of temperature, these coefficients will be further modified. An on-board temperature sensor is responsible for reading the temperature and adjusting the offset and gain coefficient accordingly. These coefficients are stored in EEPROM and used to eliminate the error value of the measurement result

3. Does this board use a voltage divider

DAQ board cards produced with outdated technology often need to be calibrated with a voltage divider. When calibrating, turn the potentiometer until the impedance eliminates all errors. There are a series of problems in the calibration of using the voltage divider: it is difficult to touch the board; Temperature drift; Defects in mechanical structure; Sudden changes. Rotating the voltage divider requires manual operation and access to the board, which will be very troublesome, because DAQ cards are inserted in the computer host, which is not easy to get. At the same time, the changing temperature will also change the impedance value of the voltage divider, so the correct calibration of the DAQ board cannot be guaranteed. Moreover, after repeated use, the voltage divider will become worn, and the connection point between the resistor element and the electric arm will be worn, resulting in an undetermined or high electric resistance, which contains unidirectional or non unidirectional reinforced material resistance. This will also lead to invalid calibration of DAQ board. In addition, slamming the partial pressure gauge will also lead to such a result. Manufacturers are also aware of such dangerous factors, so they apply a layer of strong glue on the nut to ensure the smooth progress of calibration. In this way, when manual calibration is carried out again, more strong glue is needed to prevent the screw from falling off during rotation. In practical work, these works are usually not in place, so the problem still exists. It is easy to identify whether the DAQ board is equipped with a voltage divider, because the voltage divider is large and usually bright blue, red or white

4. Does this board use multi-layer design

multi layer or multi bottom design separates sensitive analog circuits and digital signals to ensure measurement accuracy. The line that carries the analog signal to the amplifier and digitizer can detect the noise caused by the state change of the digital line. When the digital line that changes from low to high fluctuates very quickly, it will appear as a square wave in the oscilloscope. Such a sharp change is actually composed of high-frequency parts. When these high-frequency signals appear, the copper wire separated by the insulator on the DAQ board acts as a capacitor to transfer energy to the nearby line. If the surrounding line also carries analog signals, then the digital generation interference will increase, be amplified, and be digitized, resulting in inaccurate (estimated) data of gb3142 (8) 2 lubricant bearing capacity measurement method (4-ball method). Proper design can avoid this inaccuracy. The analog circuit and digital circuit are isolated in different layers, separated by copper grounding layer, so as to avoid the damage of digital interference to the analog signal. The ground plane forms a low impedance loop with the terrain of the computer, so the noise interference to the analog loop is reduced

after the concrete is leveled, the surface should be slightly higher than the mold frame by 5 How to judge whether multilayer design is used

one of the clues to judge whether a card has multi-layer design is that it is opaque. Boards with multiple ground planes are opaque because copper is opaque. Some boards will have labels or numbers of copper layers on the edges, from which you can count the layers. Some boards have multiple layers, but not the ground plane. These boards will be transparent, and you can see the lines inside. If you see lines overlapping each other, they will cause interference and noise sources

6. Does this board use SMT technology

smt technology is to connect all components to a printed circuit

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