$25,000 in Savings: How DR3421 Improved Differential Pressure Flow Measurement

Early one particularly cold morning, we noticed that our hydraulic press was cycling slower than expected. The pressure gauge showed normal readings, and the equipment had recently passed its routine maintenance checks. Yet the parts coming off the production line were consistently out of specification. At first, the problem appeared to be mechanical. But after reviewing the process data, we discovered that the real issue was hidden in our differential pressure flow measurement system. The process used an orifice plate to determine flow, but the existing measurement setup was not properly handling the relationship between differential pressure and flow. The result was inaccurate flow information being sent to the control system. After replacing the existing setup with the DR3421, we improved the flow measurement process and reduced production-related rework costs by approximately $25,000.

The Challenge: When Normal Pressure Readings Were Misleading

The first clue was simple: the pressure reading looked normal.

If the pressure gauge was showing the expected value, why were the production results changing?

We began investigating the complete measurement chain instead of focusing only on the pressure reading.

The process relied on an orifice plate to measure flow. This method determines flow by measuring the pressure difference between the upstream and downstream sides of the restriction.

The problem was that the relationship between differential pressure and flow is nonlinear.

For a typical orifice plate application:

Q ∝ √ΔP

This means that flow rate is approximately proportional to the square root of differential pressure.

If the square root relationship is not correctly applied, the control system may interpret the differential pressure signal as an incorrect flow value.

That can lead to process deviations even when the original pressure measurement appears completely normal.

Understanding Differential Pressure Flow Measurement

An orifice plate creates a pressure drop as fluid passes through a restriction.

A measurement device detects the pressure difference between two points:

Upstream Pressure → Orifice Plate → Downstream Pressure

The resulting differential pressure is then used to determine flow.

However, flow does not increase linearly with differential pressure.

For example, if the differential pressure increases by a factor of four, the corresponding flow increases by approximately a factor of two.

This is why proper square root extraction is an important part of differential pressure flow measurement.

Without it, the control system may receive a signal that does not accurately represent the actual flow rate.

For processes that depend on precise flow control, this can result in:

• Incorrect control decisions
• Unstable process conditions
• Increased material waste
• Out-of-specification products
• Additional troubleshooting
• Unnecessary rework

The Investigation: The Problem Was in the Flow Calculation

We reviewed the measurement and control system step by step.

The investigation covered:

• Differential pressure measurement
• Pressure signal transmission
• Square root calculation
• Flow signal processing
• Controller response
• Final production results

The pressure measurement itself was not the main problem.

The issue was the conversion from differential pressure into a usable flow signal.

Our existing system required additional mathematical processing in the controller to perform the square root calculation.

This created unnecessary complexity in the control architecture and increased the risk of incorrect flow calculation.

The result was a measurement signal that did not consistently represent the actual process flow.

That explained the confusing situation we had observed:

Normal pressure readings → Incorrect flow calculation → Incorrect process control → Out-of-specification parts

The Solution: DR3421

We installed the DR3421 to improve the measurement system.

One of the key reasons for selecting the DR3421 was its built-in square root extraction function.

Instead of sending a raw differential pressure signal to the controller and requiring the controller to perform the mathematical conversion, the DR3421 could handle the square root extraction directly.

The measurement chain became much simpler:

Orifice Plate → Differential Pressure → DR3421 → Square Root Extraction → 4–20 mA Signal → Controller

This approach reduced the amount of mathematical processing required by the control system and provided a flow-related output that was easier to integrate into the existing process.

Built-In Square Root Extraction

Square root extraction is particularly important when differential pressure is used for flow measurement through an orifice plate.

The raw differential pressure signal and the actual flow rate do not have a linear relationship.

The DR3421 can perform the square root calculation internally, allowing the output signal to represent the corresponding flow relationship.

This eliminates the need for separate square root processing in the controller.

For system designers and process engineers, this can provide several advantages:

• Simpler control-system configuration
• Reduced controller processing requirements
• Fewer external calculation steps
• Easier integration with 4–20 mA control systems
• More consistent flow signal processing

The result is a cleaner measurement architecture.

High Static Pressure Capability

Another important requirement was high static pressure capability.

In many industrial applications, the measured differential pressure may be relatively small compared with the overall process pressure.

The instrument therefore needs to measure a small pressure difference while withstanding a much higher static pressure.

The DR3421 supports static pressure up to 100 bar, making it suitable for applications where high line pressure and differential measurement occur simultaneously.

This is particularly relevant to industrial differential pressure flow measurement, where the transmitter must handle the actual process environment rather than simply the differential value displayed by the control system.

The Result: More Reliable Flow Information

After installing the DR3421, the flow measurement chain became more consistent.

The control system received a signal that better represented the nonlinear relationship between differential pressure and flow.

The improvement helped stabilize process control and reduce the measurement-related deviations that had been contributing to production problems.

Most importantly, the issue was no longer treated as a mysterious mechanical failure.

The measurement chain itself became easier to understand and troubleshoot.

This experience reinforced an important lesson:

A normal pressure reading does not necessarily mean that the flow measurement is correct.

The entire measurement and calculation process needs to be considered.

$25,000 in Avoided Rework Costs

The original measurement problem had a direct impact on production.

Incorrect flow information affected process control, contributing to parts being produced outside specification.

Those parts required additional inspection, rework, or disposal.

After correcting the flow measurement and square root extraction process, the facility reduced the associated production waste.

Based on our internal calculations, the improvement resulted in approximately $25,000 in avoided rework and process-related costs.

The savings did not come simply from replacing one instrument with another.

They came from improving the complete measurement process:

Better measurement → Better flow calculation → Better process control → Less rework

This is an important consideration when evaluating industrial instrumentation.

The cost of an inaccurate measurement can extend far beyond the price of the sensor itself.

DR3421 Key Specifications

• Differential pressure measurement
• Static pressure capability up to 100 bar
• Built-in square root extraction
• Wide turndown ratio
• Two-wire 4–20 mA output
• Suitable for orifice plate flow applications
• Designed for industrial process measurement and control

Applications

The DR3421 can be used in applications where pressure difference is used to determine flow or monitor process conditions.

Typical applications include:

• Orifice plate flow measurement
• Industrial flow monitoring
• Hydraulic systems
• Process control
• High-static-pressure measurement
• Filter monitoring
• Pipeline monitoring
• Pump monitoring
• Industrial automation

Why Proper Flow Calculation Matters

The biggest lesson from this experience was that measurement accuracy is not determined by the pressure reading alone.

In an orifice-based system, the relationship between differential pressure and flow must be correctly handled.

If the mathematical conversion is wrong, the control system can make the wrong decision even when the pressure signal itself looks normal.

That is why proper differential pressure flow measurement requires both reliable pressure measurement and correct signal processing.

By performing square root extraction directly in the DR3421, the measurement system became simpler and more suitable for the actual flow calculation required by the process.

Conclusion: Better Measurement, Better Process Control

What initially appeared to be a hydraulic press problem turned out to be a measurement problem.

The pressure readings looked normal, but the flow calculation was not correctly reflecting the relationship between differential pressure and flow.

The DR3421 addressed the issue by combining reliable differential pressure measurement with built-in square root extraction and high static pressure capability.

The result was a simpler measurement architecture, more reliable flow information, and approximately $25,000 in avoided production and rework costs.

For industrial processes using an orifice plate, getting the pressure measurement right is only the first step.

The calculation that converts differential pressure into flow matters just as much.

How much production waste could your process avoid with more reliable differential pressure flow measurement?

Learn more about the DR3421 and its square root extraction capability for industrial flow measurement applications.

Tags: #differentialpressuretransmitter #flowmeasurementDP #squarerootextraction #DR3421