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| Advanced Crystal Technology use the industry standard seven column specifying code systems. All the various characters of the code have a direct meaning and no translation is required. |
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| A typical specification reads like this; | |||||||||||||||||||
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| Column 1 | Frequency | ||||||||||||||||||
| Column 2 | Holder Style | ||||||||||||||||||
| Column 3 | Frequency Tolerance in ppm plus or minus (±) at 25°C | ||||||||||||||||||
| Column 4 | Temperature Stability in ppm ± over the temperature range set by the 5th column | ||||||||||||||||||
| Column 5 | Lower negative value of operating temperature range | ||||||||||||||||||
| Column 6 | Load Capacitance in pF if parallel resonance, or SR if series resonance | ||||||||||||||||||
| Column 7 | Only used when the crystal is an overtone: 3rd, 5th, 7th etc. | ||||||||||||||||||
| Frequency Generally specified in Megahertz (MHz) but can also be specified in Kilohertz (kHz). The majority of crystals are capable of adjustment to within less than 10 parts per million of nominal frequency during their manufacture, it is therefore advisable to specify the frequency to seven figures. Where our customers provide us with insufficient information, we shall generally assume that the next figure is zero. For example, a frequency given as 1.82 MHz would be taken as 1.820 MHz and not 1.82447 MHz as could required. As mistakes are expensive to correct, Advanced Crystal Technology will always require written / faxed confirmation before proceeding with customer specification orders. |
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Holder |
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| Frequency Tolerance In order to manufacture a crystal with a specific resonant frequency, the crysal must be ground to certain dimensions, the lapping of the quartz determining the frequency. There will exist some dimensional tolerance in the manufacture and therefore a fixed error, defined as the frequency tolerance, usually specified at 25°C. For most crystal applications the adjustment frequency will be between 10 and 100 ppm. |
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| Temperature Stability Temperature stability is the allowable frequency drift in ppm (parts per million) over a specified temperature range. Note that this should not be specified as the operating temperature range of the crystal as they are two different specifications. It is important not to over specify the temperature stability as this does have a direct effect on the cost of the crystal. |
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| Circuit Condition As the resonant frequency of the crystal depends to a large extent on the reactance the crystal presents to an external circuit. It is therefore important the crystal is ground to frequency at the load reactance with which it will be used in each circuit. Load conditions have become standardised, the most common being 12, 18, 20 or 30pF in parallel: where at resonance the crystal acts as an inductive reactance. Series: where, at resonance, the crystal acts as a resistor. Maximum ESR, drive level and inductance may also be specified but these parameters are generally determined by the crystal itself and evolve as standard values. However, these parameters may be modified during production of each crystal and customers' own requirements should be specified where necessary. |
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