straight line Displacement sensor The relative position (the relative position is the relative total position of the position) represents the absolute position (since the total length has been set inside, the relative position becomes the absolute position). It can not lose data after power failure and recover automatically after power on. straight line Displacement sensor Both voltage and current are analog signals. As long as the analog signal is set to zero and reference, it is generally absolute signal. These signals will not be transmitted, even if they are lost, they will not be wrong.
Before describing the problem of linear displacement sensor, we have to use a real column to explain this problem. For example, for a ktc-400mm linear displacement sensor, when the minimum position is connected to the instrument or PLC, when the output is 0vdc at the minimum position, it represents the corresponding position of 0 mm; when the position is the maximum, the output is 10VDC (or 5VDC, which will not be repeated below), which means that the corresponding position is 400mm (this is also true) It has been set by the computer. Since our position and voltage output are linear settings (which have been set in the instrument or computer), when the output is 5VDC, the corresponding position is 200 mm. Other positions are also on the straight line connected by the two points (0V, 0mm) and (10V, 400mm). Of course, there is a small deviation between the output voltage and the corresponding position, which is about ± 0.05% FS. There is another problem. If the customer mistakenly selects and installs ktc-50mm under the above-mentioned conditions, the display position and the actual position will be inaccurate. Why is that? Because the computer only knows that when setting 10 V DC, it corresponds to 400 mm. Even if the linear displacement sensor is pulled to 500 mm position, it only displays 400 mm. If the linear displacement sensor is at the output position of 5 V, that is, 250 mm, the display is only 200 mm. What shall I do? This is as long as the setting 10VDC corresponding to 400mm is changed to 10VDC corresponding to 500mm. Of course, it can also be set in reverse. 0vdc corresponds to 400mm position, 10VDC corresponds to 0mm position, and the computer works normally.
Above is the linear displacement sensor for direct 10 VDC power supply, instrument or PLC is also required voltage input. If there is no 10 V DC power supply, then generally only 24 V DC power supply, if the instrument or PLC needs voltage 0 ~ 10 VDC input, you can use external voltage module to convert the output signal of linear displacement sensor to 0 ~ 10 VDC; if the instrument or PLC needs 4 ~ 20 mA, then the output signal of linear displacement sensor will be converted into 4 ~ 20 mA signal.
But the pulse signal is different, for example: the encoder of incremental pulse (also has the digital display ruler of linear pulse), there are a, B, Z three-phase pulse signal lines, on the A, B, separately connected to a or B line (the power supply ground is the common terminal), each turn is 3600 pulses, or receiving 3600 pulses will know to rotate a circle, if there is external interference, more than a few pulses come in, less than 3600 pulses will be received in one turn, and there will be an error. Therefore, in the incremental encoder, there is a Z pulse signal, which is a check bit, that is, a pulse is given every turn to reset the data. That is to say, whether there is interference or not, there is loss of pulse signal, it is a circle. So, since phase A and phase B have output separately, why should a and B be connected at the same time? That's because if one of the direct a and B phases, whether the encoder rotates forward or reverses, the pulse will go up, so you can't tell what angle the encoder shaft is. Only a and B are connected at the same time, the forward pulse increases and the reverse pulse decreases. No matter how the encoder rotates, you will know the exact position. In this way, the function of encoder a, B and Z is clear. In addition, the original data may be lost when power is turned on again after power failure, and it needs to be reset. If the data is not lost before power failure, it needs to do very complicated work. 1. First, it needs to refresh and store the data every moment. This memory also has a backup battery (button battery). 2. The storage speed should be fast enough to keep up with the speed of the movement. For example, if 3600 pulses per revolution and one turn per second, it will rotate 3.6 pulses per millisecond, almost 4 For example, 0.25 MS, the frequency is about 4000 Hz. Even if such a technology is achieved, it is possible to miss a pulse;
Therefore, it is better to develop an encoder that does not need such complex storage, that is, the "absolute encoder". Since the absolute encoder is a unique "pulse group" identification signal corresponding to each position, such a "pulse group" signal needs to be transmitted, so it needs parallel wires The number of bits in a "pulse group" basically requires as many wires as possible. Of course, there are positive and negative power lines, and there may be clock lines and data lines. This will be explained in detail in the absolute encoder.