iWorX® ALM2
505-013, Effective: November 12, 2010
13
© 2010 Taco Electronic Solutions, Inc.
APPLICATION DESCRIPTION
The ALM2 provides alarm detection and reporting by monitoring up to eight inputs. Each input can be configured to
support a thermistor reading or a switch contact reading. Each alarm event detected is reported to the network. Digital
outputs are provided to drive external alarm indication such as lamps or buzzers, or to drive larger loads when used
with pilot relays.
Figure 5: ALM2 Application
ALM2
Each of the unit’s eight inputs can be configured to accept either digital or analog information. Digital inputs are pro-
vided from dry contact switches, and either normally open or normally closed switches may be used. Analog inputs are
provided from thermistors.
If an input is configured to read from an analog thermistor, the temperature reading is compared to a high and a low
limit. If the temperature is above the high limit or below the low limit, the controller generates a temperature alarm for
that input.
SEQUENCE OF OPERATION
This section describes the detailed sequence of operation for the controller.
Temperature Alarms
Thermistors are used for temperature inputs. The ALM2 reads the sensor and converts it to temperature once every
execution cycle. The converted value is made available as a network variable output. The temperature reading is com-
pared to two threshold levels: an upper threshold and a lower threshold. If the reading is below the lower threshold or
above the upper threshold then an alarm is generated. Four different detection methods are available by manipulating
the threshold levels.
Disable temperature detection by disabling the input.
The ALM2 also provides adjustable hysteresis on the threshold comparisons to prevent excessive alarm output jitter.
There is one “master” hysteresis adjustment for all thermistor alarm detectors, while the upper and lower thresholds are
adjustable for each input. The threshold and hysteresis adjustments are adjustable via the LCI.
Detection Method
Lower Threshold
Upper Threshold
Out of Range
Low Setpoint
High Setpoint
Over Limit
High Setpoint
Maximum Setting (230.0
°F,
110.0
°C)
Under Limit
Minimum Setting (-29.9
°F,
-34.4
°C)
Low
Setpoint
