What to consider when choosing a sensor
In this article, we will be walking you through what you need to consider when choosing a sensor to ensure your objectives are met.
Strap yourselves in
In SAPHI’s world of monitoring, automating and integrating, sensors play a fundamental role in our day-to-day when servicing client needs. We know that there are only so many people we can physically support each day to spec, configure, deploy and integrate the right sensors, so we decided to draw up a blog post to help those of you out there that have decided to tackle the journey alone.
What you will get from this article
- Accuracy of sensors – how important is it?
- How accuracy relates to price
- How do sensors capture real-world data?
- What to consider when looking for a sensor
- A word of caution
Accuracy of sensors - How important is it?
Let me reach into my development bag of throw away lines and present you with a “Well that depends” to kick things off. It sounds like a cop-out, I know, but it is hard to make universal statements in the world of tech, especially when it comes to sensors.
It is a nuanced world that requires a highly specialised skill set to assess the multitude of variables competing for attention in each project. To put it concisely, the lower the accepted margin of error, the more accurate the sensor needs to be.
Give me an example
Let’s say you are launching a rocket into space and are looking to integrate an IMU (inertial measurement unit) – a fancy term to describe those sensor units responsible for monitoring rockets’ force and angular rate – then you will want to be confident those sensors are extremely precise. A significant deviation might result in disaster!
However, if you are looking for a basic PH sensor for a tank, +/- half a PH unit will, in most cases, be acceptable.
It is all about application.
Accuracy and price
As you might have already guessed, the accuracy of a sensor tends to be proportional to the cost. The more accurate the sensor, the higher the cost. For example, take a humble turbidity sensor; prices can range from tens of dollars to tens of thousands!
The variation in price in the sensor world is extreme, so it is crucial to evaluate the value of the problem you are solving, the acceptable margin of error and commercially available options – but more on this later.
How do sensors capture real world data?
Sensors function in much the same way as the human body. Our bodies are an amalgamation of intricate sensor units that allow us to gather information on our surroundings.
For light detection, we have our eyes, sound our ears, and temperature our skin. These specialised sensors detect stimulus in the real world, convert that stimulus into an electrical impulse and send it to the brain to make sense of it and react.
Similarly, a sensor is designed to detect a change in the real world and convert it into a measurable analogue or digital signal that is sent to a processor (the brain) for processing.
Whilst this is a crude example, it serves well to offer a high-level overview of a sensor’s function. However, should you wish to go into more technical detail, check out this article.
What to consider when looking for a sensor?
As you are aware, there is a sensor for just about everything in our world. From capturing vibration, light, movement and sound through to proximity, orientation and positioning, there is a seemingly endless list of options for each category, so how do we know which one is right for us?
I should preface the following by first acknowledging that each of these sensor categories will have its own peculiarities that can only be considered within its own category.
For example, suppose you are looking for a sensor to detect movement. In that case, you need to first ask yourself what movement type you are measuring, linear or rotary. This important filtering question obviously only applies to this category.
With that said, the following broad considerations are critically important to ensure you select the correct sensor. Failure to do so can result in significant investments with no return.
1. Accuracy & Price
As previously mentioned, accuracy is often proportionate to the cost, so it is vital to assess the minimum margin of error acceptable for your project.
For example, if you are looking for a PH sensor and a margin of error of +/- 0.5 of a PH point is acceptable, then there are a whole host of pretty affordable options out there for selection.
On the flip side, if you require accuracy of 0.1<, you will be looking at a more significant investment per unit. Be sure to analyse the requirements and budget to.
It is crucial to reflect on the environment these sensors will be operating in and for how long. Are these sensors going to be sitting in a corrosive environment or tucked away in an air-conditioned office? If they are in a corrosive environment such as a sewer or water pipe network, how long will they be in there? Hours, days, months, years?
These questions are important to address when selecting the appropriate device as they will inform your team about the level of ruggardisation the sensor needs to function long-term.
The more corrosive the environment and the longer the length of deployment, the higher the IP rating will need to be.
Like with accuracy, range can have a significant effect on price, in many cases, the broader the range, the more expensive it is. A temperature sensor capturing 0-100 degrees is relatively cheap, however, finding one that can capture up to 2000 degrees is going to set you back.
To filter out the irrelevant, it is critical for you to determine the range of variance you are most interested in capturing and ensure the sensor can cater for this.
4. Data Capture Frequency
One of the most critical considerations in device specification is the frequency you need to capture data. How granular do you need the data?
Sensors will have different max frequencies that they can sample data with. The higher the number, the greater the accuracy. It is crucial to know the variability of your parameters and select a sensor that will provide the best chance to ensure those events are captured.
What do I mean by this? Well, if an important event you wish to capture happens every minute and lasts for 5 seconds, and your device only samples every minute, you have a meagre chance of catching this event.
This is because the event may happen 10 seconds after your last sample was taken and is over before the sample is retaken 50 seconds later. Hence a higher sample frequency is necessary to ensure important events don’t slip through the frequency cracks.
5. Calibration & Maintenance
How often will your team be able to recalibrate and service in-field devices? Different sensor units and types have varying recalibration requirements. This information is usually provided by the manufacturers.
6. Mounting & Mobility
How often will you need to move the sensor units? Will they serve their whole lives in a single location? Does the location allow for easy mounting?
Some sensor units can be particularly large and cumbersome, leading to difficulties in deployment and extraction. Not to mention the size of the unit may, in fact, inhibit the medium you are measuring.
For instance, if you have a water flow sensor unit that takes up most of the pipe, you will constrict the water flow and potentially cause more damage than good.
7. Availability & Reliability
When investing in vast deployments for long-term data capture, it is important to select devices with either high availability or reliability (ideally both).
If a sensor unit breaks down, you will want to be able to replace it readily. However, suppose the lead times for the units are lengthy. In that case, you will want to ensure the reliability of the sensors is such that you can expect more time in-between failures.
A word of caution
With an insatiable global demand for data and those devices used to capture it, thousands of companies have sought to capitalise. This has resulted in an explosion of devices, all marketed as “the world’s best sensor for XYZ”.
I fail to go a single week without being harassed by sensor companies worldwide trying to convince me that their sensor units will solve all my and my clients’ problems.
However, the fundamental problem with this is that most of these devices talk the talk but fail to walk the walk. Our team are regularly on the phone with new clients who reach out for support after being burnt one too many times by device conglomerates. It is deeply frustrating to witness the thousands of people having their budgets chewed up for no result when they embark on their data capture journey. All due to inflated claims.
If you take nothing else from this article other than what I am about to say, I can rest a happy person: always be sceptical of sensor company claims.
And remember – buying sensors is only half the job. Once purchased, you will need a confident team who have the expertise to program, configure and deploy the assets to ensure they reliably capture the data you value.
Thank you for reading!
Thank you for reading this article. We hope it gave you some valuable insights into the electronic product development process.
To find out more about the electronic product development process, reach out to our experienced engineers at firstname.lastname@example.org for a quick chat.
Follow our page