Configure Alarms

You can set an alarm to trip when a sensor reading rises above or falls below a specified value on certain logger models. Note: The U30 Station also has alarms capability; see Setting Alarms on a HOBO U30 Station for more details.

To set an alarm:

  1. If the Alarms window is not already open, click the Alarms button from the Launch Logger window. If there is no Alarms button, then the logger does not have alarm capability. If the Alarms button is disabled, be sure you have enabled logging on a sensor that supports alarms. If the Alarms button is disabled for MX, UX100, or UX120 series loggers, make sure the Logging Mode is not set to Burst. Alarms are not available for these loggers when the Logging Mode is set to Burst in the Launch Logger window.
  2. In the Alarms window, select the sensor that you want to have an alarm. Note: The example below is for a UX100 series logger. Any differences for other logger models are noted in these steps.

  1. Select the High Alarm checkbox if you want an alarm to trip when the sensor reading rises above the high alarm value. Type the reading next to the High Alarm checkbox or drag the red upper slider. In this example, we've set an alarm to trip when the temperature rises above 85°F.
  2. Select the Low Alarm checkbox if you want an alarm to trip when the sensor reading falls below the low alarm value. Type in the reading next to the Low Alarm checkbox or drag the blue lower slider. In this example, we've set an alarm to trip when the temperature falls below 32°F.

Note: The actual values for the high and low alarm limits are set to the closest value supported by the logger. For example, the closest value to 85°F that the UX100 series logger can record is 84.990°F and the closest value to 32°F is 32.043°F. In addition, alarms can trip or clear when the sensor reading is within the logger specifications of 0.02°C resolution. This means the value that triggers the alarm may differ slightly than the value entered. For example, if the High Alarm is set to 75.999°F, the alarm can trip when the sensor reading is 75.994°F (which is within the 0.02°C resolution).

  1. Set the duration for out-of-range samples before an alarm is tripped.
  1. Select either Cumulative or Consecutive for the Sensor Alarm Mode (select logger models only). If you select Cumulative, then the alarm will trip when the time the sensor is out of range over the course of the deployment is equal to the selected duration. If you select Consecutive, then the alarm will trip when the time the sensor is continuously out of range is equal to the selected duration. For example, the high alarm for temperature is set to 85°F and the duration is set to 30 minutes. If Cumulative is selected, then an alarm will trip once a sensor reading has been at or above 85°F for a total of 30 minutes since the logger was configured; specifically, this could be 15 minutes above 85°F in the morning and then 15 minutes above 85°F again in the afternoon. If Consecutive is selected, then an alarm will trip only if all sensor readings are 85°F or above for a continuous 30-minute period.
  2. Choose how long the logger should maintain the sensor or visual alarm once it has tripped (select logger models only). Select "Host has relaunched logger" if you want the alarm to remain visible on the LCD until the next time you relaunch the logger. Select "Sensor reading within limits" if you want the alarm to clear once the sensor reading returns to the normal range between the high and low alarm limits. Select "Cleared with button press" if you want the alarm to remain on and visible on the LCD until you press the Alarm button on the logger (select logger models only).
  3. U14-00x loggers only: You can set the Relay Contacts to Normally Open or Normally Closed as described in the logger manual. Click the Test Set Alarm button to test the relay switches. Deselect the "Set Alarm on Low Battery" checkbox if you do not want an alarm to trip when the logger's battery is running low.
  4. MX1102 loggers only: You can select Use Audible Alarm if you want a beep to sound on the logger every 30 seconds when the sensor alarm trips. The beeping will continue until the alarm is cleared from the software, a button on the logger is pressed, or 7 days have passed. Battery life will be slightly reduced when this setting is enabled. It is recommended that you only enable this feature if you have regular access to the logger so that you can easily turn off the beeping.
  5. Click OK to save the alarm settings and return to the Launch Logger window.

Once the logger is launched, alarms will trip as determined by these settings. For UA-001 loggers, a "high" or "low" LED will blink when an alarm is tripped; alarms are checked at every logging interval. For other models, logger alarms will display on the LCD screen. The alarm limits are checked when the logger's LCD screen refreshes. See the logger manual for details on LCD screen refresh rates.

When you read out the logger, high and low alarm levels will be displayed on the plot. In the example below, the temperature rose above 85°F so those readings are in the red, or high alarm, portion of the plot. The temperature never fell below the low alarm limit, which is the blue portion at the bottom of the plot. Some logger models also display alarm events showing when the alarm tripped (and cleared if applicable). In this example, there are "Chan 1 Alarm Tripped" and "Chan 1 Alarm Cleared" events showing when the temperature alarm tripped and cleared. The "Chan 1 Alarm Cleared" event contains the value that was furthest out of range for the sensor before the alarm cleared (see the Points table for the actual value).


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