Are Microwave or radar level transmitters safe to use?
Microwave level technology has become very popular in the industry to measure the material level in a variety of closed vessels. It’s easy to see why. It is virtually impervious to the changing conditions inside a tank when they are gases, vapors or even excessive dust. As a result, it finds applicability beyond other level technologies that normally suffer due to degraded performance when operating in these environments. But what about operators: are they safe when working with radar level transmitters? Is their health at risk?
So, is there a health issue?
Although the question comes up sporadically, it is fair to ask. Let’s consider something more commonplace, namely the mobile phone. We all have heard the concerns mobile phones may pose to our health. And, while they don’t necessarily dismiss or endorse the concerns, even the FCC has established limits of exposure to radio frequency radiation and provided guidelines for manufacturers to limit radiation exposure. Besides the FCC, institutions like ANSI and OSHA have also taken a closer look at the effects of radio frequency radiation.
What is the spectrum of concern for exposure limits?
Microwave frequencies occupy the upper part of the radio frequency electromagnetic spectrum, usually defined as the frequency range from about 300 MHz to 300 GHz. As you can see from this spectrum, radar level transmitters operating around 6, 25 or 78 GHz fall within this frequency range.
The exposure limits used by the FCC are expressed in terms of SAR (Specific Absorption Rate), electric and magnetic field strength and power density for transmitters operating at frequencies ranging from 300 kHz to 100 GHz. Read FCC OET informational bulletin 56 to learn about exposure limits.
What are we looking for with safety?
Radar level transmitters can handle the toughest of level applications. However, they are characterized for very low output power and low duty cycles. This results in low average power. It is the average power and not the peak power that is of a concern in terms of safety.
In addition, since the exposure to radio frequency radiation from any of these devices is not continuous, the exposure time is thus reduced. Per the FCC (per ANSI guidelines) it is permissible to exceed the limit for short periods as long as the time- average limit is not exceeded over appropriate specified time limits.
So, how do radar transmitters measure up?
In the interest of safety, all Siemens radars level transmitters were evaluated based on worst case conditions. That is, where maximum limits could be achieved, it was verified that these radar transmitters fell below the established safety limits- and way below a typical mobile GSM phone in terms of SAR values. For example, mobile phones having a SAR value of 1,000 mW/kg are considered to be below the allowable limit. By comparison, a SITRANS LR250 has a SAR value of just 0.24 mW/kg. In terms of power density, a late model domestic microwave oven is allowed to radiate approximately 2,000 mW/m2. The SITRANS LR250 emits only 9 mW/m2 at the face of the antenna.
Putting safety concerns at rest
Considering that the radio frequency radiation of radar level transmitters is well below those of domestic microwave ovens or cellular phones, we can safely say that operators should not be concerned about health issues when working with them in close proximity. Furthermore, these level devices are installed in enclosed vessels and often they are located hundreds of feet away from any operator.
Do you have concerns regarding radar in open air?