Pulse, State, and Event Data Recorders - A Guide to the Right Choice for Your Application

Although they are related to one another, the State, Event, and Pulse recorders were each designed for very different purposes in mind and meet the needs of a particular application.

  • A State Recorder: an indication of how long an event lasts

  • An Event Recorder: an indication of when an event happens

  • A Pulse Recorder: an indication of the amount of times an event happened within a specific time

These three types of units are all different and insight into practical applications of each will be provided in this article. It is important to aid the user in choosing the right product for their specific application.

State Recorder

The State Recorder is a device that measures and records a time-stamped value. This is done whenever the state of the signal is altered over a specific time. This can be a useful tool during a time when the user needs to be able to gather data on an event duration. It records the data points to show the duration of an open door; that is, the data collected informs the user that an alteration in the “state” of the door happened:

  1. When the door opened at 9:30:00 am
  2. When the door closed at 9:30:05 am

The user can calculate the duration that the door was open for a period of 5 seconds.

Note: if the leading edge of a state occurs among position 0 and position 1, the recording will show it as taking place at position 1.

The state of the input is sampled by the State Recorder at specific intervals. The change needs to be present when it is sampled for a state change to be recorded. In the case where more than one transition happens between position 0 and position 1, the state of the input at the time of the sample will be recorded independently. Consequently, it is important that the sample period must be set to under the minimum time needed for the input signal to increase and decrease. In the event that the change in state does not continue for a certain amount of time to be active at the time of sampling, it will be missed.

An additional application for the State Recorder is the monitoring of the turning on and off a furnace or pump. The State Recorder can capture these because they both have a long enough state change.

Event Recorder

When an event occurs within a fixed reading interval, a single direction time-stamped data point is recorded by the Event Recorder. This is beneficial for when the user does not know the duration of the event, but needs to be able to collect data on when an event occurred.

In comparison to the State Recorder, the Event Recorder does not deliver the data points that inform you how long the door was open. Instead, the Event Recorder has the ability to track the amount of times the door was opened, but it cannot show the duration it was open for.

For example, the Event Recorder provides the user with data about the events occurred:

  1. The door opened at 9:30:00 am
  2. The door opened at 9:37:04 am
  3. The door opened again at 12:22:13 pm

Therefore, the user can track the amount of times the door was opened, rather than how long the door was open each time.

The Event Recorder’s resolution is 1 second which means that the device can record an event every second. In contrast to the State Recorder, a persistent signal is not required for the Event Recorder and will trigger on the leading edge of the signal transition. It should be noted however, that:

An additional, frequently-used application for an Event Recorder is monitoring tipping-bucket rain gages. The Event Recorder can record data when the bucket tips up and the contact is closed. The Event Recorder will not miss recording any data points, especially because it is doubtful that the rain gage bucket will tip up more than once per second.

Pulse Recorder

The Pulse Recorder records the amount of pulses that occur over a time period. Different to the State or Event Recorder, a time-stamp for each pulse is not provided. Rather, the device groups together or ‘bins’ the amount of pulses in accordance to the time period they occurred in.

For example, if traffic through a door is being monitored by the user, the Pulse Recorder has the ability to record the regularity that the door was opened during each interval:

  1. Between 9:30 and 9:31 am, the door was opened 3 times
  2. Between 9:32 and 9:33 am, the door was opened once
  3. Between 9:36 and 9:37 am, the door opened twice

The Pulse Recorder needs a signal of 10 microsecond duration at the minimum, and at least 100 microseconds between the leading edge of each pulse to be totaled. When these specific conditions are achieved, every pulse will be recorded, up to 4.3 billion pulses per time interval.

However, records of pulses may not occur if it is under 10 microseconds, or if over one pulse occurs within a 100 microsecond time period. If the latter occurs, it is possible that additional data points are not recorded until 100 microseconds post the initial pulse.

The Pulse Recorder is widely used for pipeline applications; to measure the flow rate or total volume. The Pulse Recorder gathers pulses created by a flow meter, and uses that information to compute the number of gallons per minute. The flow meter creates a pulse that is too fast to be recorded by the Event or State Recorder, but it can easily be ‘binned’ by the Pulse Recorder. The number of pulses in a time interval is what is focused on here, rather than the exact time when the pulse took place.

This information has been sourced, reviewed and adapted from materials provided by MadgeTech, Inc.

For more information on this source, please visit MadgeTech, Inc.

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