Sorry to have been missing in action on our blog!!

We have posted a new white paper on our web site written by David Grice of ZMDI. The article, published in Sensors Magazine, is titled, "Optimizing the Calibration of Sensor Interfaces With Built-In Correction Algorithms". Here is an abstract of the article with a complete link to download.

Sensor signal conditioners with built-in correction algorithms can greatly aid sensor system designers as long as they understand which algorithm to use and when. The perennial challenge for sensor interface designers is to calibrate and correct the inherent nonidealities present in transducers. The major contributors to nonideality are typically the nonlinear response to stimulus, the offset, and the temperature dependence of one or both of these factors. The advent of commodity IC's with high-performance analog and complex digital circuitry reduces the effort and cost of sensor correction and provides the designer with systemic methodologies and tools for sensor correction. This article examines these techniques and describes how to optimize them for one broad class of sensor signal conditioners that are inexpensive yet highly configurable, enabling high-precision measurements made using a range of sensor types.

You may download the complete white paper here. No sign up necessary!

When designing a new product, looking for components can be daunting. Often times, designers must decide whether to purchase an off-the-shelf pressure sensor or design their own. This post helps clarify the criteria designers can apply when making this important decision.

• What do I need from the total SYSTEM perspective? Look at the overall product by reviewing total performance requirements, the market and applications. How does this affect component selection?
• How quickly will begin sellingyour product?
• What skills do you have within your organization? What skills do you need to outsource? For example, do you have electrical and mechanical engineering skills residing within your organization? If you do, are they accessible and available for design assistance? If you need to look elsewhere, do you have a qualified resource to utilize?
• Do you have the equipment necessary to calibrate your own transducer? Typical equipment needed are temperature, pressure and humidity tools to modify the environment for calibration. Are there people available to calibrate your designed sensor?
• There are additional logistical issues to consider. For instance, what is your annual requirement of sensors? What is your time-to-market and cost targets? Where are you manufacturing? Are there any proprietary issues to consider? How many sources do you need?

By reviewing these questions, the path to deciding between make versus buy becomes much clearer. You should buy a complete transducer if you are resource-limited and have a fast-time to market requirement. Lower volumes typically under 25,000 sensors per year do not usually warrant the investment in making your own transducer. Above this quantity, return on investment on internal resources is improved and may be something to consider.

Let's take a look at a specific example by evaluating the following situation. 

An application has a requirement for a calibrated, temperature-compensated pressure sensor that measures up to 30 psi. An amplified, off the shelf solution has a cost of between $6-7 each at 1,000 pieces, with a 1.5% to 1.8% accuracy over a broad temperature range. A fully packaged solution also translates into fewer parts to buy and stock.

To create the same transducer internally, the cost of an unamplified, uncalibrated pressure sensor plus additional op amps and signal conditioning to calibrate for span and off-set would cost in parts approximately $2-3, not including assembly labor and calibration time. Perhaps your accuracy requirements are not as stringent as 1.8% over a wide temperature range or there are packaging issues to consider. Another consideration to think about, if you are utilizing a contract manufacturer, there are typically assembly charges per component so the additional insertion of perhaps 6 components could affect assembly costs.

If your volumes are very high, investment in automated, more sophisticated calibration equipment can reduce labor time and costs and have an attractive return on investment.

Our team of experts combined with a broad selection of pressure sensors (both unamplified and fully packaged) and signal conditioning parts can guide you through this process. Our huge offering ensures that a solution can be found for you, regardless if you make or buy.

To get started, the best use of your time is to take advantage of the Sensor Selection Tool. We can then provide you with informed, detailed options for your consideration at no obligation to you. We view our role as a design resource to find you an optimal solution for your design.

Access the Sensor Selector Tool here

Review our Transducer Design Guide which includes typically sensor elements and signal conditioning for making your own pressure transducer.

This blog post was submitted by David Grice a systems architect at ZMD America.

Designing and implementing sensor interface designs for nonlinear, temperature-dependent transducers presents some difficult challenges.  The advent of dedicated and powerful Sensor Signal Conditioning (SSC) ICs has made the job easier, but choosing the right IC for a particular sensor and application is critical for making optimal performance and cost tradeoffs.  In this article we will examine some of the most important features and functions to consider when choosing the best SSC for your application.

Knowing your Sensor
The first step in choosing an SSC is to understand the characteristics of the sensor that it interfaces.  Sometimes a designer is tempted to skip this step and pick an SSC with the most powerful and complex correction techniques that are available or affordable.  This is not only wasteful in terms of cost and loading on expensive production testing resources, but often detrimental.  Depending on the intelligence designed into the correction algorithms, sometimes a higher-order equation fit will create more error than a simpler equation that more closely matches the inherent response of the sensor.  Characterizing and analyzing sensor behavior over all environments is time well spent.

The Right Partner
Before plodding through pages and pages of datasheets to understand every tedious detail of dozens of potential SSC candidates, take a step back and evaluate what level of support and overall experience the manufacturer provides with their products.  This is especially important for a product like an SSC where complex equations are used to calculate the correction coefficients.  If the manufacturer does not provide development hardware and software to automate and evaluate the calibration routines, you will be left to develop those resources on your own.   Even more important is the ability and willingness of the manufacturer to answer questions  about their product and support materials that routinely arise during the development phase.

Total System Cost
Another commonly overlooked factor in SSC selection is the production cost of calibration, especially for high-volume applications.   Sometimes a cheaper part will actually end up costing more overall because it uses an unsophisticated calibration routine that requires more time on costly testers and environmental chambers.  The ZMDI family of SSC products is designed with this in mind.  Their intelligent correction algorithms allow for “single pass” calibration that minimizes the time required for data collection and for coefficient calculation and programming.  This is a tremendous benefit and should be given serious consideration in the selection process.

Narrowing the Field
After selecting the right partner and family of products, the choice must be narrowed to an individual part.  Typically, the process of elimination is the easiest and fastest way to accomplish this.  For example, the ZMDI SSC product family is broadly divided into resistive and capacitive bridge sensor types.  If your sensor is capacitive, the candidates will be limited to the ZSC312X series.

After sensor type, the next criteria that narrow the range of products most quickly are the qualification level and environmental requirements.  For automotive level quality (AEC-Q100), the available choices  are the ZSC31150, ZSSC3170, or one of the ZSSC31xx products.  Applications that do not require automotive qualification can use any of the ZSC310xx or ZSSC30xx parts.

Once the field has been narrowed to this point, the remaining criteria for completing the selection process are operational constraints such as gain and resolution, response time, supply voltage and current, and output interface type (analog, I2C, SPI, etc.).  If multiple parts meet all these requirements, the final selection can be made based on price or special features like alarm outputs or sensor diagnostics.

Options + Process + Experience = Success!
Abundance of choice can be a double-edged sword, but a methodical approach combined with an experienced partner will make the selection process  smooth, efficient, and successful.  

Learn more about sensor signal conditioning

Servoflo has posted a new paper written by Dr. Norbert Rauch, a well-respected sensor engineer in Germany. His paper, titled "The 24-bit Revolution in Pressure Sensor Technology", discusses how altitude can be accurately measured with the impressive resolution provided in the MS5607 silicon-based pressure sensor, which uses the latest 24-bit ADC technology.

Most traditional altimeter sensors have resolution of several meters, making them not very precise. These traditional sensors have a digital signal conditioning unit and operate on a 14-bit ADC. However, a 14-bit ADC does not automatically mean that the signal can be resolved with 14 bits. Depending on the signal span, offset, and the signal evaluation electronics, possibly 10-12 bits are available for signal conditioning. Until now, achieving a better level of resolution was only achievable with a complex pressure sensing system which is costly and difficult to achieve.

The paper discusses how the MS5607 eliminates these problems with the use of an ASIC and MEMS technology. By taking into consideration that resolution must not be confused with precision, calibration accuracy and offset drift due to temperature changes must also be considered when assessing solutions. Physical size and power consumption are also factors for designers.

The paper will educate readers on how to better understand the importance of the 24-bit designs and implications for applications.

The following is a new product announcement:

The  new ZSSC3123 is a low power capacitive sensor signal conditioning IC that supports a broad range of sensor types and gives engineers a cost-effective component option for sensor designs.

With 14-bit resolution and 0.25% accuracy, the ZSSC3123 has first-pass calibration and low power consumption at 60uA with sleep mode lowering current consumption to <1uA. Target applications include low power battery driven sensor applications, sensors for humidity, weight scales, load and compression sensing, as well as tension control.

Capacitive sensors are often favored for their small size and lower power consumption. The ZSSC3123, complements these features and provides designers an optimal solution. The device is particularly suited for MEMS-based sensor elements, such as pressure sensors for hydraulic control systems, humidity sensors, and liquid level gauges. The ZSSC3123 connects to microcontrollers but can also be utilized in stand-alone designs for transducer and switch applications.

The ZSSC3123 can be configured to interface with capacitive sensors from 0.5 to 260 pF, with sensitivity as low as 125 atto-Farads per digital bit. The part can be used in both single and differential input sensor configurations. The device offers full 14-bit resolution for compensation of sensor offset, sensitivity and temperature.

Accuracy at the standard supply voltage of 2.3 to 5.5V is 0.25% over the -20C to +85C range and 0.5% from -40C to +125C. I2C and SPI interfaces as well as PDM or alarm outputs are provided.

Pricing will be available shortly.