Sterilight 254NM-468 UV Sensor

Sensors such as the Sterilight 254NM-468 are an important component to many UV systems.  A UV sensor is a device that measures the amount of UV energy that is being delivered to the water being treated.  The 254NM-468 sensor is a UV monitor assembly for SUV 400-SUV800 units.  

This UV sensor is able to detect if adequate disinfection is being achieved.  If enough UV energy is being delivered to the water, and received by the sensor, disinfection will occur and the sensor will not sound an alarm.  But if there is not sufficient UV energy being delivered to the water, the sensor will detect this and a low UV alarm will be sounded.  All NSF Standard 55 Class A UV systems are equipped with a sensor.

What Can Cause a Low UV Alarm?

There is no question that a defective sensor can cause confusing and at times frustrating false alarms.  But often, the sensor is simply doing it's job in detecting a situation where low UV is being delivered to the water.  What can cause this?

Water Clarity

In order for proper UV disinfection to occur, the water that is being treated must have a certain optical clarity.  That is, the water must be able to allow the UV light to pass through it and reach the organisms that one is trying to destroy.  

If the water is muddy, disccolored or cloudy, it may not let enough light pass through for proper disinfection to occur.  This is more common in surface water sources than it is in ground water.  In order for the UV system to work properly, the UV Transmittance (the measure of optical clarity to UV light) must be greater than 75%.  UV manufacturers will test this water parameter for free if you submit a water sample.

Fouling

All water sources contain minerals.  Ground water supplies usually have a higher mineral content than surface water supplies.  Different water sources will contain different minerals.  Common minerals found in drinking water supplies are calcium, magnesium, iron, and manganese.  When these minerals come into contact with a UV system - especially the warm quartz sleeve that surrounds the lamp - they will be deposited.  

Over time these deposits increase in thickness and may get to the point where they block the UV light being generated by the UV lamp.  If this happens, the sensor will detect low UV and will sound an alarm.  If you suspect a faulty sensor it is always a good idea to clean the quartz sleeve and sensor window before buying a replacement UV sensor.