AMETEK 7100 Leak Detect Stik - Manual (Page 14)

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Chapter 3: Getting the Data
The method that data is communicated between the probe and the console is described in Section 1.1: Data
Protocol. The user should understand the data protocol scheme before attempting to process the data.
3.1: Synchronizing with a Watchdog Timer
Referring to Figures 1 and 5, note that there is only one pause period per frame and therefore, only one
time during the sequence when no pulses will be received for approximately 9 milliseconds. A hardware or
software watchdog timer may be implemented to time-out after 7 milliseconds (for probes > 18’, this time
should be 14 milliseconds) which will occur only during frame #1, the pause frame. The next 15 pulse pairs
may then be recorded in the sequence shown in Figure 1.
NOTE: The times depicted in Figure 5 are not exact times³. A watchdog timer setting of 7 milliseconds should
generally be used.
3.2: System Hardware Setup
Before discussing signal processing, a brief review of the console hardware is in order. Refer to Section 2 as
required.
Based on a 16 foot maximum probe length, the number of bits required for the probe counter circuit is the
duration of the low reference temperature pulse pair. With a 3 ms low reference pulse duration and a 100
MHz clock frequency, the number of bits can be calculated. Dividing the low reference pulse pair duration by
the period of the clock yields 300,000 counts. Converting this number to hexadecimal will show the number of
required bits. In this case, 19.
³ Although the time between adjacent frames is generated with an internal crystal oscillator, the actual pulse pair for a temperature
frame is delayed a few hundred microseconds nominally. This is independent of any temperature data. The product and water float
pulse pairs may be delayed as much as 2 milliseconds. This delay is affected by the corresponding float position. The longest delay is
experienced with a long probe with the float near the bottom.