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Model 421-A Temperature Alarms are microprocessor-based dual-setpoint temperature alarms that are suitable for environmental and industrial applications. This system sensor heat detector can also be configured as a frost alarm. It sounds an alert and controls the operation of two electrical circuits whenever the temperature reaches either of two independently set limits. The temperature range is -40° to 160° F (-40° to 71° C) and the alarm range is the same. The temperature alarms can be selected to operate either greater than or less than the selected temperature output. A liquid crystal display provides readout of the measured temperatures and is also used to display maximum and minimum temperatures as well as the values of the various alarm parameters using a series of setup menus.
Self-contained relays for each alarm point can be used to actuate external devices such as small pumps or sirens. These internal relays may be used to control external power relays if high current loads are to be switched. An audible alert, which may be silenced if desired, is also included within the Model 421-A Temperature Alarms. To eliminate erratic or premature operation of controlled devices, the Model 421-A system sensor heat detector includes provision for setting a delay or conformation interval prior to the initiation of an alarm and also a delay time prior to negating an alarm.
All setpoints and maximum and minimum temperature values are stored in non-volatile memory so that these values are not lost if there is a power failure. The circuits are designed to have high electrical noise immunity to transient spikes generated by loads being switched with the temperature alarms' relay. The system sensor heat detector restarts in the running mode after a power failure.
Temperature sensor: Precision thermistorMeasurement range: -40° to +160°F (-40° to +71°C)Alarm range: -40° to +160°F (-40° to +71°C)Resolution: 0.1°Accuracy: ± 0.5°F (± 0.2°C)Alarm ON and OFF delay range: 0-99 secondsControls: Protected push buttons that selectRun or set variablesSelect menu itemIncrement alarm settingDecrement alarm settingClear stored max and min valuesIndicators: LEDs for alarm point 1 and 22 line x 16 character LCDDisplay character size 3x8 mmOperating temperature: Control module only -20° to +50° CInput power: 12 Vac or dcCurrent: 50 mA maximumAlarm: Contacts rated 3A @ 24 Vdc/115 VacForm "C" (SPDT) configurationTemperature cable length: 40' 2-conductorWeight/Shipping: 1 lb/2 lbs