The Model 221R has become the standard oxygen deficiency monitor throughout the US market. It is used by the thousands in government labs, universities, and industry, anywhere there is a possibility of asphyxiation due to leakage of compressed or liquefied inert gases like nitrogen, argon or carbon dioxide.
It has become the standard because it is extremely reliable, does not drift even with extreme temperature swings or barometric pressure changes and does not generate false alarms but responds very rapidly to real oxygen emergencies.
Competitive monitors that use conventional electrochemical sensors suffer from serious false alarms issues. Electrochemical sensors lose sensitivity over time – requiring monthly calibration - and typically after about a year need to be replaced. These sensors suffer from pressure and temperature sensitivities that cause them to drift into alarm when weather patterns change or even when air conditioning systems cycle, even though the actual oxygen level is safe.
The model 221R offers a number of compelling features that make integration into building or plant alarm systems easy.
It provides two alarm relays, operating in fail-safe mode that provide up to 110V at 5A switching capability. They respond to the standard OSHA alarm levels of 20.0% warning, 19.5% danger, and they also respond to a 23.5% over-enrichment situation.
The front panel status LED changes color when an alarm occurs, and when a danger alarm occurs the built-in audible alert sounds. This alarm can be temporarily silenced.
It can be calibrated using a known clean air sample, but it only needs calibration bi-annually, and then mainly in order to verify its calibration.
It provides an isolated 4-20mA output corresponding to the oxygen reading that can be monitored by an analog control panel.
It provides a bi-directional RS-485 communication system that can monitor all the internal parameters and even download a data log of readings over the previous fifteen days.
It can be mounted on a wall, and hosed down. It is available with a remotely mounted oxygen probe, so that the display and alarm can be seen outside a room while the air within the room is monitored, so personnel may be kept out when conditions are dangerous.
It contains enough batteries to allow it to continue operating up to an hour after power failure, and it will indicate an alarm for a period before the batteries completely die.
Finally – we use a number of these in our own plant in places where we keep liquid nitrogen Dewars.