Rangeability and turndown ratio are fundamental characteristics of pressure transmitters. Simply put, rangeability refers to the ratio between the maximum and minimum pressure a pressure transmitter can accurately measure. Turndown ratio, often synonymous with rangeability, specifically indicates the maximum capacity of a measuring device in relation to its minimum measurable capacity.
Summarize this article with :
Are you wondering what the terms " rangeability " and " turndown ratio" mean in a pressure transmitter ? Do these technical terms seem confusing to you, and you're looking for some clarification?
In this article, we'll delve into understanding rangeability and measurement dynamics in pressure transmitters. We'll explain what these terms mean, why they're important and how they affect the operation of a pressure transmitter.
We will also explore related concepts such as maximum and minimum pressure capabilities, the importance of measurement range, and how the concepts of rangeability and measurement dynamics can be applied.
Rangeability, commonly referred to as turndown ratio, is a critical parameter in control systems, especially when it comes to process pressure transmitters . Whether it's the turndown ratio of a differential pressure transmitter , a gauge pressure sensor or an absolute pressure transmitter , it's a simple formula that compares a device's maximum measurable range with its minimum measurable range.
This ratio is often expressed by a number such as 3:1, 5:1, or even 100:1, indicating that the sensor is capable of accurately measuring pressures within this range. For example, in a sensor with a turndown ratio of 5:1, if the maximum pressure (the upper limit) it can measure is 100 units, it can accurately measure up to 20 units, which is its lower limit.
The range measurement is the maximum pressure range over which the pressure transmitter can operate. It extends from the minimum pressure (lower limit of the measurement range)to the maximum pressure (upper limit of the measurement range) that the pressure transmitter's sensor can measure, e.g. from 0 to 100 bar.
The upper limit of the measuring range (URL) refers to the highest pressure for which the sensor has been designed to measure, within the upper limit of the cell.
The lower measuring range limit (LRL) refers to the lowest pressure for which the sensor has been designed to measure, within the lower measuring range limit of the cell.
The upper range value (URV) is the maximum pressure at which the pressure transmitter is calibrated or set. It corresponds to the highest point on the output scale, such as the 20 mA point in a 4 to 20 mA output signal.
The Lower Range Value (LRV) is the minimum pressure at which the pressure transmitter is calibrated or set. It corresponds to the lowest point on the output scale, such as the 4 mA point in a 4 to 20 mA output signal.
The calibrated or setspan is the operating range equal to the upper range value (URV) - the lower range value (URL). It is equivalent to the analog output signal from 4 to 20 mA.
The measuring dynamic or rangeability (TD) of a pressure transmitter is calculated by dividing the maximum pressure the device can measure (the upper limit of the URL measuring range) by the minimum measuring range it can measure accurately (minimum measuring range). The evaluation of measurement range and performance for pressure transmitters is governed byIEC 60770-1 test methods.
In mathematical terms:
Measurement dynamics (TD) = upper limit of measurement range (URL) / minimum measurement range (URV-LRV)
For example, suppose a given pressure transmitter has an upper measurement range limit of 100 bar and a minimum measurement range of 10 bar.
Using the formula, the turndown ratio would be 100 bar/10 bar = 10:1.
Turndown ratio, an essential aspect of any pressure measurement devicesuch as those with a 4 to 20 mA output signal, describes the extent of the difference between the highest possible measurement range and the lowest possible measurement range. The turndown ratio defines an adjustable range within the measurement range. This ratio is fundamental in defining the functional bandwidth of sensing instruments, and plays an essential role in their operational flexibility and accuracy.
The rangeability of a given pressure transmitter depends on several factors.
One of the most important is the maximum pressure the sensor can tolerate without being damaged or its performance diminishing, otherwise known as the upper measuring range limit (URL). This is the maximum pressure capacity at which the device can operate safely.
Another influencing factor is the minimum pressure, the lower limit of the measuring range (URL) , which is the lowest pressure level the device can accurately measure.
These two factors depend on the characteristics of the sensor's measuring cell and cannot be modified.
The final factor is the pressure transmitter's measurement range, which has a major influence on rangeability and measurement dynamics. This measurable range is defined as the range between the upper value of the calibrated or set measurement range (URV) and the lower value of the calibrated or set measurement range.
Understanding rangeability and turndown ratio is essential in many applications where pressure must be monitored and controlled. This is particularly important in fluid and gas control systems, where accurate measurement and maintenance of pressure levels are paramount to successful operation.
You'll find everything you need to know about the rangeability and turndown ratio of a pressure transmitter, including how these attributes affect the accuracy and efficiency of a pressure measurement system.
Choosing a pressure transmitter with the right turndown ratioc can have a significant impact on the accuracy of readings and, consequently, on overall system performance. For example, if your application requires a measurable and controllable pressure range between 50 and 100 units, a sensor with a turndown ratio of 5:1 and a maximum pressure rating of 500 units would not be suitable. Its minimum measurable pressure would be 100 units, which would not cover the lower end of the required range.
However, if the same application uses a sensor with a turndown ratio of 10:1 and a maximum nominal pressure of 500 units, the minimum measurable pressure would be 50 units, which would perfectly cover the required range. The result would be more accurate readings and better process control.
Turndown ratio and rangeability also play an important role in calibration.
Calibration is the process of adjusting the analog output of a pressure transmitter so that it corresponds exactly to the measured pressure. To do this, the instrument is compared with a reference measurement standard by generating a pressure of known fluids.
This operation involves calibrating the transmitter's high value (maximum pressure SPAN) and low value (minimum pressure ZERO) to ensure accuracy.
Turndown ratio indicates the range over which the pressure transmitter can be calibrated or adjusted. A pressure transmitter with greater turndown ratio can be calibrated more finely over a wider range of pressures. This means that a transmitter with greater turndown ratiooffers a wider calibration and adjustment range, giving it greater flexibility in a variety of applications.
An essential feature of intelligent pressure transmitters (SMART) is their readiness to be re-ranged without the need for calibration. Unlike analog instruments, which can only be re-scaled by re-calibration, the measuring range or span of digital sensors can be adjusted after manufacture at the factory, or on site, after initial installation.
In digital instruments, calibration and scaling are usually separate settings (i.e. it is possible to change the scale of an intelligent pressure transmitter without having to perform a complete recalibration).
So, if your process requirements change, you can adjust the pressure transmitter's range and zero point to meet the new requirements without having to replace the measuring device.
Scaling an instrument involves setting the upper and lower scale values so that it reacts with the desired sensitivity to variations in the pressure input.
For example, if a pressure transmitter has a reduction ratio of 10:1 and was initially calibrated at the factory for the maximum pressure range of 10 bar (0 bar = 4 mA output; 10 bar = 20 mA output), you can readjust it on site from 0 to 1 bar (0 bar = 4 mA; 1 bar = 20 mA) to accurately measure lower pressures.
Conversely, if a sensor has a turndown ratio of 10:1 and was initially calibrated for the minimum pressure range of 1 bar (0 bar = 4 mA output; 1 bar = 20 mA output), you can readjust it up to 10 bar (0 bar = 4 mA; 10 bar = 20 mA) according to the new requirements.
This re-ranging or scaling capability, directly linked to turndown ratio, can significantly improve the longevity and adaptability of the device to process characteristics. This makes it a valuable asset in any pressure monitoring or control system.
Although high measurement dynamics may seem desirable because of their flexibility, it's important to bear in mind their limitations.
Very high turndown ratio may promise a wide operating range, but measurement accuracy may decrease and degrade at the lower end of the measurement range.
In this case, a pressure transmitter with more modest rangeability, better suited to real-life operating conditions, can provide more accurate results.
Understanding the rangeability and turndown ratio of a pressure transmitter is essential for correct set-up, accurate measurement and efficient control of your processes involving gases or liquids. These parameters not only have an impact on the accuracy of the device, but also on the safety, efficiency, flexibility and overall performance of your system.
Take advantage of the knowledge you've gained about rangeability and turndown ratio and use it to optimize the performance of your pressure transmitters. Don't forget that choosing a pressure transmitter with the right rangeability and turndown ratio for your specific application is an essential step towards accurate pressure regulation and measurement. Now you can make an informed decision. Keep exploring!
While a high measurement dynamic provides flexibility in pressure measurement, accuracy can decrease at the very low and very high ends of the range. It's essential to choose a transducer with a measurement dynamic that matches the specific pressure requirements of your system. Consult a pressure transmitters manufacturer like Fuji Electric to help you determine the sensor best suited to your application.
Yes, many pressure transmitters offer a rescaling capability, allowing you to adjust their calibrated measurement range after initial setup. However, the extent of the adjustment depends on the measurement dynamics of the device.
No, measurement dynamics vary from one pressure transmitter to another. This is an important parameter to consider when selecting a transmitter for your specific application. Fuji Electric's FCX pressure transmitters offer measurement dynamics of up to 100:1, making them particularly flexible in use.
Although measurement dynamics is an important parameter, its importance varies according to the application. In systems where pressure levels vary significantly, or where small fluctuations can have a major impact on performance, high measurement dynamics are generally beneficial. In systems where pressure levels are stable, lower measurement dynamics may suffice.
A transmitter with high rangeability can handle a wider range of pressures, which may reduce the need for multiple transmitters. However, the decision depends on a number of factors, including the system's specific pressure requirements and the accuracy required at different pressure levels.
Discover the incredible performance of our highly rangeable electronic pressure transmitters . Thanks to their remarkable turndown ratios, our pressure transmitters offer unrivalled accuracy and flexibility for pressure measurement in a wide range of applications.
Benefit from the advantages of accurate pressure measurement, whether to optimize processes, reduce downtime, guarantee product quality or improve safety. Our highly rangeable pressure transmitters enable you to meet the demands of varying pressure conditions, all with a single device.
