(Editor's note: Originally published on EDN.com)
It may seem intuitive that field service engineers needing a handheld spectrum analyzer require one that is designed for field use, yet surprisingly few handhelds are designed to address all of the rigors the outdoors has to offer. Understanding what field engineers want from a handheld spectrum analyzer requires a scrutiny of the environmental realities faced in the field.
Military standards are often referenced by manufacturers as a means of illustrating the durability of a device. For electrical test equipment, such as handheld spectrum analyzers, MIL PRF 28800T defines the “performance characteristics required for an intended location of use and the most severe prevailing environmental conditions of such locations.”
Handheld equipment falls under Class 2 of the standard. To meet Class 2 requirements, the device “is designed for rugged operational environments where the environmental conditions are routinely encountered in an unprotected, uncontrolled climate.” See Figure 1.
Figure 1. MIL PRF 28800 Class 2 compliance provides a benchmark of durability.Venting frustrations
The measurement environment can pose numerous challenges, particularly for handhelds with external vents. For example, making measurements in arid regions often exposes handhelds to dry and dusty conditions. Handheld vents provide a pathway for particles to enter the unit and in worse case scenarios, the intruding materials can render the handheld inoperable.
Rain and humidity are other potentially detrimental environmental conditions. Vents create the opportunity for devices and components inside the instrument to be exposed to moisture. If exposure occurs when current is flowing, a malfunction can occur, potentially compromising the integrity of measurements.Hot and cold reactions
Scientific studies conducted by Helsinki University of Technology have found that the productivity of indoor employees is optimum between 72 °F (22 °C) and 77 °F (25 °C). Rarely do field engineers work in such ideal conditions. Depending on the job, field engineers, and their handheld spectrum analyzers, are called to work in the frigidness of the arctic, to the sweltering heat of the dessert, and the range of temperatures in between these extremes.
While all handheld spectrum analyzers are designed to work over a wide range of temperatures, the fact that the unit works is not the only consideration. What is critical is that the unit’s functionality is maintained to specifications and that it remains fully-calibrated over the manufacturer-specified operating temperature range.
In between jobs, the handheld signal analyzer is typically thrown in the cab of a service vehicle. Over lunch breaks or at work sites where it is not needed, the unit will typically stay in the locked vehicle. Then, consider this: according to the Journal of the Louisiana state Medical Society, the inside of a car parked on a cloudy, 85 °F day in 53% humidity can reach around 160 °F in just one hour. This reality is why the storage temperature range specifications for a handheld become an important consideration. Dropping expectations
Field-rugged handheld spectrum analyzers need to withstand much more abuse than simply being tossed in a vehicle cab. Since the job frequently necessitates engineers traverse rough terrain in order to obtain measurements it’s reasonable to conclude that the unit will occasionally fall in transit and be dropped on the work site. Another jolting nemesis to handhelds is prolonged vibration caused by transport such as on a helicopter or truck traveling over rough roads. A unit’s compliance to MIL PRF helps ensure that the device can withstand this abuse and still provide accurate and reliable performance.Power demands
All handheld spectrum analyzers are powered by batteries that have a finite life. A key differentiator of handheld spectrum analyzers lies in what action needs to be taken in order to restore power to the unit. Engineers that have found themselves at a remote location with a handheld that has run out of power understand the importance of having a unit where the battery pack can be easily changed in the field (see Figure 2). Another consideration is how, or if, the battery can be re-charged. Ideally, recharging batteries doesn’t require the battery be shipped back to the manufacturer. Using handhelds with batteries that can be recharged at the service depot is cost-effective, environmentally responsible, and convenient: benefits that are also important to managers of field operations.Figure 2. Re-chargeable and field-replaceable ensure batteries are readily available and there’s always enough power ensure site work gets completed. >>Page Two: Displays, Keys, Planning Tools, Comfort (on EDN.com)