Accurate and reliable level and pressure measurement are critical to safe and efficient industrial process control. In harsh industrial environments, these measurements often rely on the mechanical transfer of process conditions to a remote transmitter.
Capillary-based diaphragm seals have traditionally filled this role. However, they can also introduce accuracy and maintenance challenges. As facilities push for higher reliability, tighter quality control, and reduced maintenance, the limitations of capillary systems become increasingly apparent.
Digital diaphragm seals eliminate many of these vulnerabilities.
Top Reasons Process Control Measurements Become Unstable
Capillaries are often the hidden weak point in level and pressure measurement.
Capillary-based diaphragm seals are designed to protect pressure instruments like gauges, transmitters, and switches from harsh process media. They work by separating the instrument from the process fluid with a flexible diaphragm, while a fluid-filled capillary tube transfers pressure to the sensor.
Core failure and performance risks associated with capillaries include:
Temperature Effects on Measurement
The fill fluid expands and contracts as temperatures change. Outdoor conditions can cause the reading to drift even when the process stays the same, leading operators to think the process is changing when it isn’t.
Response Lag
Long capillary tubes physically delay the pressure signal. The longer the run, the more lag. This slows measurement, hides real process changes, and makes operators chase “ghost” fluctuations.
Mechanical Vulnerability
Capillary tubing is prone to kinks, vibration-induced fatigue, and incidental damage during maintenance. Each of these can change the fluid volume or stiffness, distorting readings without other obvious external signs.
Installation Variability
The length, routing, bends, and heat exposure of capillary tubing all affect performance. Even installations that appear identical can include small variations that lead to different measurement results.
For operators and maintenance teams, these issues don’t always look like capillary problems. Instead, they show up as symptoms, such as:
- Inconsistent level readings
- Frequent recalibration
- Apparent process noise
- Operator distrust in measurement systems
As these inconsistencies accumulate, control loops become increasingly difficult to tune. Yield and quality suffer, and maintenance teams spend more time validating instruments than supporting operations.
How Digital Diaphragm Seals (DDS) Improve Process Control Measurement
Compared to traditional capillary systems, digital diaphragm seal systems are better because they are more accurate, faster, and easier to maintain.
Rather than relying on a mechanical transfer of pressure through a fluid-filled tube, digital diaphragm seals digitize the process signal at the diaphragm itself and transmit data electronically. This offers:
Higher Accuracy
Digital systems are not affected by temperature changes like capillary fluid is. This means more reliable pressure readings.
Faster Response Times
There is no long capillary tube filled with fluid, so the measurement responds instantly and more reliably to pressure changes.
Lower Maintenance
Traditional capillaries can leak, kink, or degrade over time. Digital diaphragm seals have fewer mechanical parts, reducing failure and downtime.
Improved Performance in Extreme Conditions
They work well in variable pressures, vibrations, and long distances where capillary systems struggle.
Easier Installation and Flexibility
Digital signals can be transmitted over long distances without loss, unlike capillary systems that require careful routing. Without fragile tubing to route and protect, instrumentation installation becomes more predictable.
Learn more from ABB, our manufacturer partner. Read ABB’s report on Digital Diaphragm Seal systems.
Industries Where Digital Diaphragm Seals Deliver the Most Value
Digital diaphragm technology can be used in many industries, but it is especially useful where accuracy and reliability matter the most.
- Chemical Processing
Handles corrosive media and temperature changes with fewer mechanical issues, reducing calibration and downtime. - Oil & Gas
Remote sites exposed to harsh weather can see more stable readings and spend less time troubleshooting. - Power Generation
Frequent temperature changes and critical control loops benefit from faster, more stable measurements. - Food & Beverage
Clean installations and repeatable batch processes benefit from consistent performance and low maintenance. - Pharmaceuticals
Reduces recalibration and documentation burden, and offers higher confidence in validated level measurements.
Transition from Legacy Capillaries to Digital Diaphragm Solutions with ABB
Replacing legacy capillary-based systems with digital diaphragm solutions doesn’t have to be disruptive.
Because modern digital diaphragm transmitters often support standard communication protocols like HART (widely used across control systems) they can be dropped into existing architectures without extensive redesign.
What is HART Protocol?
The HART (Highway Addressable Remote Transducer) Protocol is a widely used, open standard communication protocol in industrial automation that superimposes digital signals onto traditional 4-20mA analog loops, allowing for two-way communication without needing new wires.
On the shop floor, this translates into faster commissioning, less troubleshooting, and ultimately more reliable operations.
ABB’s Digital Diaphragm Seal systems deliver more stable level and pressure measurements, reduced maintenance, and improved long-term reliability compared to traditional capillary systems.
We've expanded our partnership with ABB to give you better access to high-quality instrumentation, fast support, delivery reliability, and a stronger local team.
ABB 266 HART Pressure Transmitters with Digital Diaphragm Seal
The ABB HART 266 Digital Diaphragm Seal (DDS) pressure transmitters are designed to address the same challenges as conventional remote seal systems – while also eliminating many of the performance compromises and high costs traditionally associated with them.
The 266 Digital Diaphragm Seal (DDS) pressure transmitter is an ideal solution for reliable level and pressure measurement of filling quantities in containers, silos, and tank systems where ambient temperature effects and fast response times are critical.
The DDS simplifies measurement by integrating two direct-mount gauge sensors – one on the high side and one on the low side – that operate independently.
Key features:
- Ambient conditions that no longer influence accuracy
- Faster responses in cases of process control actions
- Lower installation costs
- Lower maintenance and replacement costs
- Modularity of the electronics and displays
Help your engineers and operators focus on the process, not the problem.
Talk to an MCE instrumentation and process control expert today.
Improve Level and Pressure Measurement Accuracy with MCE
Capillary-based diaphragm seals have done the job for a long time, but they also introduce potential issues from temperature effects, slow response, and installation variables. By digitizing the signal closer to the process, ABB digital diaphragm seals remove uncertainty.
MCE collaborates with ABB to help engineers, managers, and maintenance teams optimize performance with quality equipment, expert application support, and responsive service.
We offer:
- Instrumentation Calibration
- Diaphragm Seal Assembly & Testing
- Critical Spares Access
- Phone Support for Troubleshooting and Diagnosis
Let us know how we can help improve your processes today.