What factors are related to the oscillation amplitude and frequency in position adjustment

The basic concept of position adjustment Position adjustment is also called continuous adjustment, named after the presence of position element relays or non-contact switches in the system. Position adjustment system is a kind of nonlinear system. During its adjustment process, there will be a stable and continuous oscillation process (even if it is an unstable oscillation process, it will diverge to a stable continuous oscillation process). The three-position adjustment system will also produce Oscillation decay process. The output of the position adjustment system generally appears in the form of relay contact action, but also in the form of non-contact electronic switches.
   The task of position adjustment is to amplify the difference between the measured value and the given value into the action of the relay contact.
   Figure 1a is the adjustment characteristics of the two-position adjustment instrument, and Figure 1b is the adjustment process of the two-position adjustment system.
 
    Figure 1 Two-position adjustment
   When the measured value is 0, higher than Qa, the relay is released, and when the measured value of 0x is lower than Qb, the relay is closed. Usually the difference between Qa and 0b ΔQ=Qa-Qb is called insensitive zone or dead zone or switching difference, and (Qa+Qb)/2 is called switching median, switching median and set value 0. The difference is called the control point deviation Qε.
     It can be seen from Figure 1 that the two-position adjustment process is a stable and continuous oscillation process, and the adjustment deviation fluctuates back and forth within the range of Δ0 without a certain value; the insensitive area of the regulator directly affects the oscillation amplitude of the adjusted parameter In order to prevent the oscillation amplitude from being too large, the insensitive area should not be too large; but the insensitive area should not be too small, otherwise the operating frequency of the relay will be too high and its service life will be reduced, or even the relay cannot work, so it should be reasonable Adjust the insensitive area of the meter. It can also be seen from Figure 1 that if the insensitive area remains unchanged, the time constant of the adjusted object will decrease dramatically, and the oscillation frequency will increase. Therefore, the positional adjustment is suitable for objects with a large time constant. It works at a lower frequency in the insensitive area. In addition, if the adjusted object has a lag time t, it will increase the oscillation amplitude, which is unfavorable. Therefore, positional adjustment is only suitable for occasions where the object lag is small. Of course, if the lag time t is large, the oscillation frequency can be reduced; It can also be seen that when the time constant of the adjusted object is constant, the given value Q, or the disturbance changes, the oscillation amplitude and frequency also change. If the insensitive area remains unchanged, the relay oscillation frequency can be reduced.
    It can be concluded that the effect of position adjustment depends not only on the performance of the instrument itself, but also on the characteristics of the object to be adjusted and the quality and level of the operating personnel of the instrument. For a skilled instrument user, even if the adjusted object cannot be changed, the adjustment quality can be improved by adjusting the parameters of the instrument, and vice versa.
    Of course, in general, it is always hoped that the oscillation amplitude of the positional adjustment system is as small as possible, so that the fluctuation range of the adjusted amount can be reduced and the adjustment can be improved. At the same time, it is always hoped that the oscillation frequency is as small as possible, so that not only can the degree of fluctuation of the adjusted amount be reduced, but also the number of pull-in times of the bit-type element can be reduced, thereby prolonging the service life of the bit-type element, and for the two-position adjustment For the instrument, these two indicators are mutually restrictive and cannot be considered at the same time. If a three-position adjustment instrument is used, the situation will be greatly improved, as shown in Figure 2.



     Figure 2 Three-position adjustment
     a) Regulation characteristics b) Transition process
     Figure 2a is the adjustment characteristics of the three-position adjustment instrument, and Figure 2b is the transition process curve of the two-position adjustment system.
    Figure 2a shows the characteristics of a three-position regulator that does not consider hysteresis. In the figure, Q.1 and Q are the lower limit and upper limit set value respectively. Q is the average set value. 2ΔQ is the middle zone of the three-position regulator. According to the different value range, the three-position regulator has The so-called wide intermediate zone and narrow intermediate zone.
   It can be seen from Figure 2 that when the input QQ02 of the regulator is greater than 0.1, the regulator output is 0 and the system stops heating. Due to the object’s inertia lag, the furnace temperature begins to drop after a period of lag time. When it drops to o<02, the high relay is turned on again, heating at 1/2 of the full power, and the furnace temperature rises again. /2 can make the furnace temperature rise above the set value Q0, and the adjusted amount will continue to oscillate under Q.2-L; if 1/2 of the full power cannot make the furnace temperature rise to the set value Q0, the adjusted amount will be at Q01 , Oscillates up and down continuously; if 1/2 of the full power can just keep the furnace temperature at a given value of 0, or Q01＜Q, it can be seen that the three-position control system will have a stable continuous oscillation process, and may also attenuate Oscillation process. Even in the continuous oscillation process, the oscillation amplitude is smaller than that of the two-position adjustment. Therefore, the three-position adjustment is higher than the two-position adjustment.
It is not difficult to see from Figure 2b that the oscillation amplitude and frequency of the three-position adjustment process are still related to the intermediate zone of the adjustment instrument, the object lag, and the regulator input.