I am often asked about wireless sensors in a GMP environment and their application. They are a very attractive option for retrofitting an existing facility because they are easy to install, tailor to the requirements, affordable and don’t require expensive cabling or wall penetrations. The following details will help you determine your requirements in this emerging area.
There is a vast amount of data we collect from our facilities these days and an ever-increasing range of devices to collect and transmit this data. Retrofitting hard wired devices is expensive and disruptive, however many suppliers have instruments that can be interfaced into a wireless sensor network.
What to look for
There are a number of things to look for when investigating implementing a wireless sensor network within your GMP facility.
From a hardware perspective, you should consider the following:
|-||What to look for||Definition||Requirements|
|Radio frequencies (RF)||The frequency band the sensors transmit on||There are various devices available that operate on different RF bands. Typical frequencies include 2.4 GHz, 900 MHz and 433 MHz. The different frequencies have different pros and cons but most are unlicensed frequencies that can have congestion problems (particularly the 2.4 GHz band). Some manufacturers employ frequency hopping and other technologies to combat interference from other wireless devices. Also, the higher the frequency, the poorer the signal will travel through building walls (signal propagation).|
|Network topology||The physical arrangement of devices (sensors, repeaters, receivers) and flow of data in the wireless sensor network||Various topologies are available including star, mesh or hybrid topologies. Whichever topology is chosen, ensure it supports self-healing of failed links. The topology may be dictated by performing a detailed site survey (see below).|
|Site survey||The physical exercise of determining signal strength levels at a given location||A site survey is critical for determining whether a wireless sensor network will work within your facility and should be done during the planning stage. It will measure the signal strength between the proposed base station (receiver) location and proposed sensor locations. Some manufacturers provide dedicated equipment for completing a survey whereas others will use standard sensors and monitor signal strengths. Either method is fine, as long as the survey is completed and results are satisfactory.|
|Repeaters||A physical device that receives and re-transmits a sensor’s data to the base station or receiver||These devices are usually required to ensure reliability of sensor networks in large or physically challenging facilities. The sensors will use the repeaters as a stepping-stone when transmitting their information to the base station or receiver. The required amount of repeaters should be identified during a site survey.|
|Battery/mains power||The physical method of powering the sensor||Some brands of sensors are battery powered, some are mains powered. It could be argued that having mains powered sensors defeats the purpose of wireless however existing facilities will have numerous power outlets which can be used while also saving on battery maintenance. Whichever option is selected it’s important to:|
|On-board memory||Any physical memory installed in the sensor for logging data||Some sensors offer the ability to log data locally in the event of signal loss however, not all will automatically backfill the data gap in the main database once the link re-establishes. Different manufacturers offer different capacities. On-board memory capacities are typically measured in kilobytes or number of samples.|
|Security||Methods employed to protect the transmitted data||Some manufacturers encrypt transmitted data while others transmit using proprietary protocols. Most manufacturers have additional levels of protection including algorithms and tamper evaluation routines that will ensure information wasn’t altered and has been protected against unauthorised retransmission.|
|Calibration||Check and/or rectify the accuracy of any instrument giving measurements||As with traditional wired sensors, wireless sensors will need to be calibrated when used in a GMP environment. Frequency of calibration should be determined by risk classification however, wireless devices shouldn’t need special treatment. Physical access to the sensor and the method for adjustment should be taken into consideration when choosing instruments.|
Pros and cons of wireless sensors
From a software perspective, you should ensure the software supplied with the sensors is 21 CFR Part 11 and/or Annex 11 compliant. If it is not, some manufacturers offer gateways (e.g. MODBUS gateway) to make the data available to a compliant SCADA system.
The following pros and cons should be considered when selecting wireless sensors for your facility.
|Relatively well priced compared to a traditional wired sensor||Additional maintenance activities (e.g. scheduled battery replacement)|
|No cabling, wall penetrations or other installation difficulties||Signal propagation issues can be caused by interference, and physical obstacles (walls, personnel, equipment), particularly when changes are made in facilities, such as installation of new equipment|
|Attractive option for retrofitting existing facilities||Communication speed/reliability may not be sufficient for sensitive or time critical applications|
|Particularly suitable for sterile facilities where cabling can cause cleaning and contamination issues.||Wireless sensors by different manufacturers may not be interchangeable due to differing RF bands, proprietary protocols, etc|
A detailed risk assessment should form part of any GMP system installation, however there are a few extra things to consider with a wireless system, such as:
- How secure is the system? Any data that travels via wireless has the ability to be intercepted. It could be worth consulting with the IT department because if wireless is already in use, they may have already performed a detailed risk assessment on the use of wireless within the facility. There may be many reasons why some companies or departments see wireless as too big of a risk.
- What will happen to the data if the signal drops out? Obviously the risk of data loss exists even with traditional wired sensors however the likelihood of this occurring with wireless could be higher. You will need to consider if the data affects product quality and how release will be effected if there is a data failure. Keep in mind that data corruption is highly unlikely, for example a 22.4°C signal will not become 32.4°C, rather you will just be left with a gap in your data. This is where on-board memory and self-healing of failed links could benefit.
- How will changes in the facility impact the wireless signals? When new equipment is added within your facility, you may need to revalidate the wireless signals in the area to confirm that the new equipment isn’t causing interference.
Validation considerations Making up your mind
Compared to traditional wired sensors, there are a number of extra validation considerations to address. Depending on the results of your risk analysis, these could include:
|Validation of signal strengths||Verify signal strength at IQ against the values obtained during the site survey or have a predetermined level of acceptance (e.g. > 60%). It is also important to periodically revalidate these signal strengths at predetermined intervals, or when changes occur in the facility to ensure there is no degradation in signal strength (intervals should be determined by risk assessment).|
|Verify signal loss||Is an alarm generated when then signal drops out?Is the data automatically backfilled when communication is restored (if available)?|
If automatic backfilling of data is not available then the process of manually retrieving the data it should be validated.
|Reliability||In comparison to wired sensors, there can be reliability concerns usually related to signal issues of wireless sensors. It would be worth considering extended PQ testing where reliability is validated (e.g. > 99.8%). This could be evaluated over a period of time and be defined by:|
Making up your mind
Wireless is a great option for retrofitting existing and new facilities, however it also comes with greater levels of risk assessment, validation and scheduled maintenance.
As wireless sensor technology and features increase and prices continues to decrease, there will likely be expanding acceptance of wireless sensor in GMP facilities.
The FDA has developed a guidance document on Radio Frequency Wireless Technology in Medical Devices which, although related to Medical Devices, has some excellent general information on wireless systems and technology for all regulated environments.