The most important element of the ceramic capacitive technology is the ceramic (Al2O3) measuring cell. After assembly, the ceramic cell element resembles a plate capacitor with a reference electrode and a measuring electrode placed 0.01 mm apart. The capacitance is inversely proportional to the distance between the electrodes. As pressure is applied, the distance changes by a small value and the capacitance changes proportionately. This signal is then converted into pressure by a microprocessor.
Tank level on CIP skid
Pressure sensors are used to monitor tank level on CIP skids. Often, these sensors are fitted diaphragm seals which are fragile and easily damaged. What if you didn’t have to worry about diaphragm fill fluid leaking into your process?
The direct process measurement via the PI’s ceramic capacitive technology offers an accurate solution in a robust package.
Transmitters are used to monitor line pressure in various sanitary applications. Traditional blind transmitters do not provide visual feedback and are often mounted next to a mechanical gauge. What if you could eliminate the need for a gauge?
The LED display of the PI family operates at full brightness, even in a 2-wire loop powered configuration.
With IO-Link, process sensors have the ability to transmit multiple sensor values. Via IO-Link, the PI family can provide:
Q. Why does my pressure sensor show a value without any pressure applied?
A. Typically, this is an indication that the measuring cell has been damaged and most likely due to pressure spikes. In these cases, the offset is 25 – 35% of the measuring range of the sensor. Because of the structure of our measuring cells, our Quality / Warranty Evaluation Team can diagnose a cell damaged by pressure spikes with 100% certainty.
Q. How do pressure spikes occur?
A. A pressure spike (or water hammer) is a surge of an incompressible fluid that is forced to stop or change direction suddenly. It commonly occurs when valves are opened or closed very quickly. The easiest way to understand the concept is to compare the fluid with a train. When a train is stopped suddenly, the back of the train carries momentum with it, continues to move forward for some time and sends a shock wave throughout the train. Since the water flow is restricted to the inside of a pipe, a shock wave of incompressible liquid travels through the pipe at much higher pressure than the typical system pressure.
This chart represents pressure changes over time. It shows clearly that pressure spikes can be 10 times or more than the system pressure.
Q. Can ifm pressure sensors detect these spikes?
A. No. Even though the PI family has a “Hi” and “Lo” memory to store the highest and lowest measured values, pressure spikes generally have a very short (in the nanosecond range) duration. The response time of our pressure sensors is 1 – 3 milliseconds.
Q. How can I protect my pressure sensors?
A. There are several ways:
Q. What is meant by turn down ratio?
A. This is minimum difference between the analog start point and analog end point of scalable transmitters. ifm’s PI transmitters have a turn down of 1:4 (shown on our datasheets as “programmable 1:4”.) This means that the smallest span the transmitter can have is 25% of the measuring range. For example, if the full range of the sensor is 10 bar, the minimum span is 2.5 bar, i.e. 0…2.5 bar, 1…3.5 bar, etc.
Q. How do I interpret the accuracy specifications on the datasheet?
A. The most important thing to keep in mind when calculating the deviations is that they are all referenced with a turn down of 1:1. This means that regardless of how the transmitter is scaled, the specifications are based on the full range of the sensor.
For example, the switch point accuracy is ± 0.2 % of full range. In the example above, if the range of the sensor is 10 bar, the accuracy is ± 0.02 bar. It does not matter if the transmitter is scaled 0…2.5 bar or 0…5 bar or 0…10 bar.
Q. What does “Characteristics deviation” mean?
A. “Characteristics deviation” is our most all-inclusive measure of accuracy. It includes linearity, hysteresis and repeatability.
Q. How does the process connection system work?
A. The PI family uses a flexible process connection system known as Aseptoflex Vario. The system provides more sealing options to meet the current 3A sanitary requirements. In addition to an o-ring seal (either FKM or EPDM materials), we offer a PEEK sealing ring. This PEEK ring provides longer stability compared to traditional elastomers that become hard and brittle over time.
Q. Why do some fittings for the Aseptoflex Vario system have holes in them?
A. The leakage ports, or weep holes, are required for 3A authorization. When an o-ring is in place (see above), the process medium will remain in the tank or pipe. If that o-ring is compromised, i.e., missing or damaged, the process medium will leak at the weep hole. This is an indication that the o-ring must be replaced.