SysAdmin/Transform-Expressions.md

@@ -44,3 +44,20 @@ There are couple other optional but often important parameters that can be enter
 
 Also note that all readings that use this pulse count transform are time-stamped at the midpoint between the current reading time and the previous reading time, since the rate reported is derived from the interval spanning those two time points.
 
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+If your pulse counter is setup to reset to zero after it reports its pulse count (Monnit wireless pulse counters 2013 and before), a different Transform function must be used to convert the counter values into rates.  This is not the preferred method for setting up a pulse counter but may be needed for those counters that do not have a count accumulation mode, as described in the prior section.
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+The screenshot below is example of configuring a counter that resets to zero after each sensor report.
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+[[images/transform_ex3.png]]
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+The text `count_rate` must be entered into the `Transform or Calculated Field Function Name` box.  Then, additional parameters are entered into the `Function Parameters in YAML form` box.  Each parameter has a default value, so they are not required to be entered, but you will likely need to override some of the default values.
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+**`slope`** (default value = 1.0)  
+**`offset`** (default value = 0.0):  BMON will automatically convert the incoming pulse count into a rate of pulses per second.  The `slope` and `offset` parameters are used to convert this pulse rate into the desired engineering units, such as Btu/hour or kW.  The final value stored in the sensor database is: `(pulse rate per second) * slope + offset`
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+**`typical_minutes`** (default value = 30.0, measured in minutes):  Sensor transmissions are sometimes missed or occur multiple times due to poor signal strength.  The BMON attempts to correct some of these problems but needs to know what the *typical* spacing is between sensor transmission.  Enter that value expressed in minutes for this parameter.
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+**`no_zero_after_link`** (default value = `True`, other possible value is `False`):  If a Monnit wireless sensor is having difficulty communicating with its gateway, it will sleep for two hours and then try to reestablish contact.  When it does this, it will send an initial count of zero.  By setting `no_zero_after_link` to `True` (the default value), these zero readings will not be stored in the sensor database.
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