Corporate Updates/Events

Troubleshooting the FS1650 Alarm

Problem Solving Tips – FS1650

If the FS1650 alarm is not operating properly, please use the following tips to identify and resolve the issue(s):

1. Face velocity good, alarm LED “RED”audible alarm continuously on

2. Face velocity good, alarm LED “RED”, audible alarm intermittent

3. Face velocity bad, alarm LED “GREEN”, no audible alarm

3. Alarm is not turning on, NO “GREEN” OR “RED” light indication.


  1. A quick visual check may be performed to verify that the thermistors are not broken or shorted. This is the most common with the center measuring thermistor. It may become broken from damage that occurred during installation or cleaning. Due to its small size and sensitivity, the wires connecting it to the sensor’s PCB can become broken or bent. If the measuring thermistor has a broken wire, this will result in an open circuit. Either condition will cause a continuous alarm.
  2. Establishing the appropriate face velocity is one of the most important factors in the overall performance of the enclosure. Most vented enclosures from Flow Sciences are designed to operate with a face velocity of between 60 and 100 lfpm (0.3 – 0.5 m/s) and a recommended face velocity of 75 lfpm ± 5 lfpm (0.38 ± 0.02 m/s).


Flow Sciences recommends the face velocity alarm be set at 20% below the operational face velocity. Therefore, if 75 lfpm (0.38 m/s) is the desired velocity, the alarm should be set to activate at velocities below 60 lfpm.


Begin alarm calibration by first setting face velocity to desired alarm activation velocity. Remove the four screws located on the face of the alarm. Next, set the delay to desired time by adjusting the delay screw.  Flow Sciences recommends setting this all the way to the right (30 seconds) so quick disturbances in the face velocity will not trigger the alarm.  Adjust the set point screw (shown in the image below), until the RED and GREEN lights toggle between each other. This sets the alarm so that a consistent (30 seconds) face velocity of, for example, less than 60 lfpm (0.3 m/s) will trigger the alarm.

3. If this guide suggested a replacement or your issue(s) remain unresolved, please call our office at(800) 849-3426and ask for Technical Support.

Industrial Hygienist / Product Manager

Cameron Faulconer is an Industrial Hygienist with a wide breadth of experience, spanning between commercial manufacturing, to home residences. His inspiration for his choice of career is communicating the value of preserving the health and safety of employees using the most effective and efficient means possible. Therefore, Mr. Faulconer found his place in the “Engineering Controls” rung of the hierarchy of hazard controls.

As a problem solver, Mr. Faulconer believes that the best safety solutions are created through consultative conversations with those who seek solutions. He believes communicating information derived from these conversations to be critical to the continued understanding of the toxicological impacts of the work environment.

His personal motto is “protecting the safety and health of employees from what can and cannot be seen with the naked eye”.