The PTT accessory seems to get less attention in terms of proper testing and verification of requirements than the mobile device. It is understandable that the PTT app is the centerpiece of the PTT over LTE project as the platform for communication, and therefore has a longer evaluation cycle during the evaluation phase. Often the only checkbox for the PTT accessories is compatibility to the mobile device and PTT application but there is far more to consider otherwise the PTT accessory can become a costly and administrative nightmare.
The work environment has a major influence on how rugged the accessory needs to be. This goes hand in hand with the mobile device as reasons for failure are very similar to those of mobile devices such as dropping and exposure to dirt and water. Nevertheless, since the goal is to leave the mobile device in a pocket or holder while communicating through the accessory, the ruggedness evaluation of the accessory is even more important than for the mobile device.
Noisy work environments near machines or heavy tools are an important reason to use a PTT accessory especially a remote speaker mic (RSM) as mobile phones or tablets are not able to provide the sufficient volume output. There are two measures that need to be considered when comparing the sound quality of two speakers.
- Volume Output: Volume output is measured in decibels (dB) at a certain distance (usually 10 cm = 4 in) indicating the loudness of a speaker.
- Intelligibility: Intelligibility is the measure of how well the voice can be understood. Some speakers are designed for a high output but the speech being amplified, is barely comprehensible when at the maximum level. Intelligibility, which is a science by itself, has different standards. One of the most accepted standards is the Speech Transmission Index (STI) which is measured on a scale from zero to one, predicting the likelihood of what percentage of words or sentences would be understood. The International Organization for Standardization (ISO) and the National Fire Protection Association (NFPA) have adopted the STI in their fire alarm standards.
Source: International Electrotechnical Commission. (2011)
Both volume output and intelligibility should be indicated as the measure of the accessory. Some manufacturers simply provide the specification of the speaker manufacturer which shows little understanding of RSM design as water and dust-tight housings have a significant impact on these measures. It should be noted that these measures can only be used to narrow down speaker selection. The final comparison should always happen with the devices in the real work environment during the most extreme use case.
Thanks to high speed LTE or WiFi networks that are capable of streaming video and developments in voice codecs, it is possible to have wideband PTT accessories that offer much higher voice quality than a regular phone call which is still at low bit rates. To benefit from the wideband audio quality provided by the PTT application, the phone needs to be paired with the right PTT accessory that supports wideband audio, otherwise the benefits of the well-designed PTT app voice codecs will be eradicated by a low quality audio accessory.
There are different criteria to look for depending on the work environment. Some ruggedness testing is standardized with IP ratings or MIL-STD 810G while others are manufacturer defined.
This is probably the most important test for a PTT accessory. Drops are by far the most common reason for failure. Many drop tests are manufacturer specified but dropping a device once from 1.5m (5ft) doesn’t make for a real use case. In the duration of a year, a device will probably be dropped more than ten times. A proper drop test should be done from at least 2m (6ft 7in), several times in different angles.
Dust and Water
How dirty and wet the environment can be for a PTT accessory to withstand, is covered under the Ingress Protection (IP) standards. The IP number is composed of two numbers, the first referring to the protection against solid objects and the second, against liquids. The higher the number, the better the protection. Most mobile devices already fulfill an IP67 standard and so should the PTT accessory. An IP56 or lower has proven inadequate in most work environments (except offices) for both mobile phones as well as PTT accessories.
The US military in a combined effort of Army, Navy and Air Force, has put together a comprehensive testing manifest that includes all kinds of tests military equipment might go through in its service life. There are a total of 29 laboratory test methods and some PTT accessory manufacturers have adopted some of the testing specifications to design their device against.7 Depending on the use case, some might be more relevant, such as high or low temperature tests while others might be less relevant such as pyro shock or gunfire shock. What is important to know is that some OEMs label their products “MIL-STD tested” even when successfully testing only one of the 29 testing specifications. It is therefore important to check which testing requirements meets your use case the best. Test specifications should be aligned with the most common failures of devices.
High and low temperatures as well as temperature changes, can be a challenge to any PTT accessory. Check the operating temperature of a device to ensure that the temperatures in your region are covered and consider extreme use cases such as having the accessory sit inside of a vehicle in the summer. Look out for MIL-STD-810G standards 501.5, 502.5 and 503.5.
Even if you have chosen a PTT accessory which fully matches your environmental requirements, it will not protect it 100 percent from breaking. If you have chosen a device that meets your requirements and it fails nevertheless, due to a manufacturer defect, you want to make sure that you can return it, to get a replacement or your money back. Look for manufacturers that are based or have at least operations in Europe. European law requires a two year warranty compared to the one year standard in North America.
Intrinsic safety (IS) is a protection technique for safe operation of electrical equipment in hazardous areas by limiting the energy, electrical and thermal, available for ignition. Intrinsic Safety (IS) devices can be used in explosive environments without the risk of igniting combustible elements. IS approved devices are commonly used in industries like mining or oil and gas. A communication solution, made up of a mobile phone and a PTT accessory are not intrinsically safe unless both devices have been approved. Unless it is a Bluetooth accessory, an IS approved mobile phone and a separately approved wired accessory together, do not constitute an IS approved solution. ATEX/Ex regulations are used in the European Union. The specific approval received for a particular phone will determine in which zones, environments and temperatures it can be used.
Battery Life / Charging
If the PTT accessory is assigned to one single worker who works eight hours, any PTT accessory would probably do the job. If used for two or three shift cycles by multiple workers, the battery life needs to be tested. This is also required for the charging behavior. How often does the device need to be charged and for how long? Will this time be sufficient to last for the next shift? Something else to consider is how and where the PTT accessories will be charged and the logistics involved around the charging process.For example:
- Manufacturing: How and where will 100 workers charge their mobile devices without having 100 cables flying around?
- Transportation: Is there a convenient way to charge a device in a truck? Can the device be used while charging? Is it in a location that follows driving regulations where the driver can reach the device without bending over or changing their driving position?
One of the main reasons to use PTT accessories is because workers have to wear safety attire like suits, gloves, or hearing protection. In these cases, it is even more important that a PTT accessory extends the phone’s or PTT application’s features to avoid removing safety attire to access the phone.
Protective suits: Can the PTT accessory be worn outside the suit withstanding the exposure to potentially harmful substances? Can the PTT accessory withstand cleaning or even decontamination processes?
Gloves: Can the PTT accessory be operated with protective gloves?
Hearing protection: Is the audio accessory loud enough to still be heard in noisy environments with hearing protection?
How does the accessory help the worker to stay focused on the job and provide safety features in case of an accident? The more the accessory allows the worker to communicate without accessing the phone, the less distraction communication will provoke. In addition, a Bluetooth accessory can provide communication capabilities even when separated from the mobile device. For example, a common mobile device in all kinds of trucks or construction vehicles is a tablet allowing the display of bigger maps for routing and task management purposes, however the cumbersome size makes working while carrying it an obstacle. With a Bluetooth accessory, the driver can still communicate with a Bluetooth RSM while leaving the tablet inside the cabin. Safety features such as an emergency button need to be implemented by the PTT application. The extended range of Bluetooth Low Energy allows the trigger of an emergency signal even when voice communication is not available anymore.
For more guidance on evaluating PTT accessories for your PTT over LTE solution, including crucial user features and functionality, download the complete Whitepaper for free!