Chapter 6: Using the Web Interface144Setting Data LoggingThe EMX can store 120 measurements for each sensor in a memorybuffer. This memory buffer is known as the data log. Sensor readings inthe data log can be retrieved using SNMP.You can configure how often measurements are written into the data logusing the Measurements Per Log Entry field.Since the environmental sensors are measured per second, specifying avalue of 60, for example, would cause measurements to be written to thedata log once every minute. Since there are 120 measurements ofstorage per sensor, specifying a value of 60 means the log can store thelast two hours of measurements before the oldest one in log getsoverwritten in the log.Though the environmental sensors are measured per second, theirreadings may not be updated per second. See Information aboutUpdate Interval (on page 145). The update interval varies depending onhow many environmental sensors are connected to the EMX device andthe sensor type. The more the environmental sensors are connected, thelarger the update interval is. Therefore, type a large number in theMeasurements Per Log Entry field when there are a large number ofenvironmental sensors connected.Whenever measurements are written to the log, three values for eachsensor are written: the average, minimum and maximum values. Forexample, if measurements are written every minute, the average of allmeasurements that occurred during the preceding 60 seconds along withthe minimum and maximum measurement values are written to the log.Note: The EMX device's SNMP agent must be enabled for this feature towork. See Enabling SNMP (on page 298). In addition, using an NTPtime server ensures accurately time-stamped measurements.Enabling Data LoggingBy default, data logging is enabled. You must have "Administrator" or ""permissions to change the setting.To configure the data logging feature:1. Choose Device Settings > Data Logging. The Data Logging Optionsdialog appears.2. To enable the data logging feature, select the "enable" checkbox inthe Enable Data Logging field.3. Type a number in the Measurements Per Log Entry field. Valid rangeis from 1 to 600. The default is 60.4. Select the environmental sensors whose data logging you want toenable.
