Just as there is no overall best product in general, there is no overall best pressure sensor. Although you can pay top dollar for certain features and functions, virtually every feature in one area commands a compromise in other areas. So, it is not about what is the best pressure sensor, it is all about making a smart choice! To choose the right pressure sensor for a particular application, it is important to
- Fully understand the application and the specific demands on instrumentation
- To understand some of the key terminology that sensor manufacturers use, as well as some of the limitations of sensors currently on the market.
- To combine the two and determine the ”sweet spot” for your specific situation
Understanding the application
Is vital to being able to specify the right instrumentation for the job- especially when it comes to crucial questions like accuracy and error. We have discussed this in an article (Pressure Sensor Fundamentals: Interpreting Accuracy and Error) that you may find helpful when answering those questions and reviewing your particular application. A previous article (Introduction to Pressure Measurement) we discussed how to navigate through the sea of choices ranging from a raw sensor element costing a few dollars to a so called “smart” transmitter costing thousands of dollars and pointed out that a smart transmitter is not always a smart choice.
It is discussed that it pays to spend the extra time to determine the right class of instrument for a particular job (instead of spending extra money for an unnecessary product- or underspending and risking the success of the project entirely). This article also helps how to read the data sheets and more importantly to read between the lines. Once you have all the facts, you are equipped for the final, and probably the most difficult, task — to apply those facts to your specific application.
That is sometimes easier said than done, and involves a dilemma: Should you play it safe, over-specify, and pay the additional price? Or can you make a smart choice by striking the right balance between what is really needed and what is added as a “comfort factor”? The difference can easily be worth a thousand dollars or more on a single instrument. With the sheer endless selection of products, and very little standardization in place, this task can become quite a challenge. Just as there is no overall best car, there is no overall best pressure sensor. A Lamborghini may seem like the perfect car to some — but if you want to get three kids to school and put a bike in the trunk, it is inadequate, no matter how superior it may be in other respects.
The same is true for pressure sensors — although you can pay top dollar for certain features and functions, virtually every feature commands a compromise in other areas. Here is some food for thought/ aspects to consider when selecting the right class of instrument for the job: A display for local read-out, useful and informative on the one hand, increases the instrument’s size and power consumption, reduces its operating temperature range, and is susceptible to mechanical damage, shock, and vibration.
Do you really need it? When and how is it used? Can you put a dollar value to it? Additional software features make life easier and enhance functionality, but also drastically increases the probability of (user and design) errors. It requires processors, memory chips, and many other components that reduce reliability and may shorten instrument life. How often are those features used? Do they need to be present in each instrument in the field? How about updates or different firmware/ application software version? How about connectivity in the field/ manuals/ training of operators and field technicians? Can you manage and document what is out there in the field and how you take care of it? Even seemingly simple features, such as linearization and active temperature compensation, not only have a price tag — they can also result in other behaviors that are not described in any datasheet and may have dramatic consequences that could render the device completely useless. Why? In analogue sensors and transmitters, the circuitry used is not only very robust and fairly simple- it also relies for its function and accuracy on a very few (passive) components.
Those have not only a very low failure rate and long-term stability, they also provide typically a very ”soft” failure mode, i.e. they show a slight deviation of value due to ageing but virtually never show any erratic or volatile behaviour. So even if they “fail” the function is often only slightly compromised, the process does not get out of control. Once you go “active” or use digital/ smart methods, this picture changes completely. If something fails the outcome is hardly predictable anymore and can be very disturbing- leading often to a total loss of control. The result? If doing an FMEA (Failure Mode and Effects Analysis) any digital circuitry or software requires a complete re-think of the system design and results in even more complex system architecture requiring redundancy etc. that now needs to actively “catch” any glitches and error modes that could happen to prevent the process to get out of control if a component fails. But does it pay off? It certainly does in most cases.
This is especially true if you are selecting instruments for a new design, for a series of applications or even for serial production- as any mistake, as well as any savings or overspendings will multiply with the number of instruments put out in the field. More information on pressure sensors and its application can be found in our Learning Center on electronic sensors.