Frequency difference is crystal under specified operating conditions relative value difference between the actual value and the standard value or frequency reference value frequency. Generally expressed in ppm (10-6). The main difference to adjust the frequency and temperature frequency difference. Adjust the frequency deviation is the reference temperature and the product under the specified load capacitance measured at a frequency relative to the nominal value of the frequency difference. Frequency refers to the maximum temperature difference relative frequency over the entire operating temperature range from the reference temperature frequency. The total frequency difference is the sum of the two.
       Circuit designers to adjust the frequency difference may only be prescribed, but for the entire operating temperature range of application requirements to control the frequency difference, in addition to adjusting the frequency difference given the frequency difference should give the entire operating temperature range. Given the frequency difference, should give full consideration to equipment caused by temperature tolerance.
      There are generally two methods provides the entire operating temperature range of frequency difference.
     1) provides total frequency difference
      For example, from -10 ℃ ~ + 85 ℃, the total frequency difference of ± 50 × 10-6, usually this method is generally used instead of having a relatively poor broadband frequency tuning applications.
     2) are given to adjust the frequency difference and temperature frequency difference
     Such as the frequency difference between the reference temperature (usually 25 ℃) was under ± 10 × 10-6; within a temperature range of -30 ~ + 60 ℃, relative to the frequency difference between the reference temperature of the actual frequency of ± 20 × 10-6. This method is commonly used in the more stringent frequency difference, need to rely on the frequency pulling load capacitance to eliminate the reference temperature frequency difference occasions.
      The temperature curve is parabolic BT-cut crystal, the frequency difference can be specified as a positive reference temperature tolerance, e.g. + 50 × 10-6.
  Generally speaking, it should be to determine the scope of work and the frequency tolerance of the crystal element circuit system according to the requirements.