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Version 1.73 Copyright © 1997 Link Communications Inc. 1/18/97
105: Set Analog Alarm Hysteresis
Hysteresis is a concept not everyone is familiar with, so let me illustrate it before I try to
explain how to use it. Let us suppose that you are using one of the analog lines to read the
temperature inside of your radio shack. In the winter, you want the controller to automatically
turn the heater on and off to keep the temperature above 40 degrees. To do this you decide to
control the heater with a relay that you can switch with one of the output lines. Next you set a
low alarm at 40 degrees and program the low alarm macro for that analog line to turn the heater
on and speak the message "low alarm". Now you need a way to turn the heater back off. To do
this you use the analog alarm to normal macro to turn the heater off and speak the message
"low alarm clear". This is where Hysteresis comes in. Do you want the heater to turn off at 41
degrees? This would probably make the heater turn on and off really often. It might be better
if it warmed up to 45 degrees before the heater turned off, so it would turn on and off less often.
The amount that it has to warm up past where the low alarm point was is the amount of
Hysteresis, in this case 5 degrees. In the case of a high alarm (such as would be used to run an
air conditioner, the amount of Hysteresis is how much the temperature would have to drop
below the high alarm point before the alarm to normal macro would be executed. The amount
of Hysteresis is the same for the high and low alarms (if this is not acceptable for your
application, let us know). This command lets you set how much Hysteresis each analog line
uses when determining whether the alarm is clear yet.
<105> l wwww
Parameters:
- 105 is the default command name.
- L is the analog input line number (1..5)
- WWWW is the alarm point with leading 0s if necessary
Notes:
The value you enter must be a positive number and will have as many assumed decimal places
as you set with Command 101.
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