The biochemical incubator has a high temperature control accuracy. Generally, the temperature control error is not more than + 0.5. There are many factors affecting the temperature control performance of biochemical incubator, which should be seriously considered in the design and maintenance. In this paper, the influence of temperature measurement elements in the temperature control system of biochemical incubator is studied.
1. time constant of temperature measuring element
The temperature measuring element reflects the temperature in the machine and feeds the feedback temperature signal to the input of the temperature control system. The temperature measuring element and biochemical incubator air heat exchange to sense temperature, with thermal inertia, so that when the temperature changes of biochemical culture box, temperature sensor output f (theta temperature indicator) change always lags behind the temperature theta o, T time constant temperature element 2 reflects the thermal inertia of the size. T 2 is bigger, more serious lag. Thus, the real time temperature indicator theta f obtained from the temperature measuring element is not actually the true temperature theta o in the biochemical incubator, and there is a difference between the two. Figure 1 shows a biochemical incubator temperature jump interference in order (5 C) under the action of the internal temperature the true value of theta o (T) (measured by PN junction thermometer) and a temperature detecting element measured value of theta f (T) (measured by electric contact mercury thermometer) comparison of transition process (the set temperature. I =30 C, temperature curve coordinates and 30 DEG C value delta theta). It can be seen from figure O and theta theta (T) f (T) curve of the same period of two, and tend to the same stable value, the difference is o theta (T) amplitude than theta f (T) is much larger, the highest in the biochemical culture instantaneous temperature reached 30.8 degrees, and in in this case the temperature measuring element indicates the value is only 30.2 DEG C. This shows that much more than changes in biochemical culture temperature components reflected the true temperature of the box to change the temperature of the indication, but they differ depending on the degree of temperature sensor time constant T 2, it is big, small is small. Biochemical incubator temperature measurements between the true value and this can not directly see the difference, be sure to pay full attention in the practical work, because sometimes although the temperature measuring element indicating or recording the temperature value is required, but in fact the true temperature over a period of time in the box has been far beyond the specified range. The greater the time constant of a temperature measurement element, the more serious the situation is.