DR3421 Differential Pressure Transmitter

The DR3421 Advantage: More Reliable Orifice Flow Measurement

When a hydraulic press starts cycling more slowly than expected, a normal pressure reading does not always tell the full story. In one application, the pressure gauge showed normal pressure levels, yet the press was operating below its expected cycle performance. Further inspection revealed inconsistent process results, leading the maintenance team to investigate the differential pressure measurement system used for flow monitoring.

Why Orifice Flow Measurement Requires Accurate Differential Pressure

Orifice flow measurement is based on the relationship between differential pressure and flow rate. When fluid passes through an orifice plate, the differential pressure generated across the restriction is related to the square of the flow rate. In practical applications, this means the flow calculation cannot simply use differential pressure as a linear value. The square root of the measured differential pressure must be extracted to obtain an accurate flow signal. If square root extraction is missing or incorrectly configured, the resulting flow calculation can deviate significantly from the actual process condition. This can affect DCS control, process stability, and equipment performance.

Finding the Problem in the DCS System

During the investigation, the maintenance team identified an incorrectly configured transmitter on a critical process line. The existing setup measured differential pressure but did not properly perform square root extraction for flow calculation. As a result, the DCS was receiving pressure information without correctly converting the differential pressure signal into a representative flow value. The issue highlighted an important point in orifice flow measurement:

Accurate differential pressure measurement is only part of the solution. The measured signal must also be correctly processed for flow calculation.

How DR3421 Improves Orifice Flow Measurement

The team upgraded the measurement point with the DR3421 Differential Pressure Transmitter. DR3421 combines differential pressure measurement with high static pressure capability and built-in square root extraction for flow applications. This allows the transmitter to process the differential pressure signal according to the relationship between pressure difference and flow. With the square root output available, the DCS can receive a flow-related signal without relying entirely on external signal processing. This simplifies system integration and helps reduce the risk of calculation errors caused by incorrect signal configuration.

Supporting More Consistent Process Control

After integrating DR3421 into the system, the pressure measurement point was recalibrated and the flow calculation was reviewed. The improved measurement setup provided more consistent flow information to the control system, helping the engineering team fine-tune the hydraulic press operation and investigate variations in process performance more effectively. For applications where flow is calculated from differential pressure, the quality of the measurement chain matters:

Orifice Plate → Differential Pressure → Square Root Extraction → Flow Signal → DCS Control

An error at any stage can affect the final process result.

Key Features of DR3421

• Differential pressure measurement
• High static pressure capability
• Built-in square root extraction for flow
• Wide turndown ratio
• Two-wire 4–20 mA output

These features make DR3421 suitable for process applications where differential pressure is used to determine flow, particularly systems based on orifice plates.

A Practical Question for Your Flow Measurement System

If your process uses an orifice plate for flow measurement, check how the differential pressure signal is being processed.

Is square root extraction performed correctly in your transmitter or DCS?

A reliable differential pressure signal combined with correct flow calculation can make a significant difference in process monitoring and control.

Tags: #DR3421