How DR3702 Solved EMI Noise in Hydraulic Presses

Our hydraulic press was cycling slower. The gauge showed normal pressure, but the parts were consistently out of spec. This issue wasn’t new; it had plagued our operations for months, costing us significant downtime and scrap. In fact, we estimated the total cost exceeded $50,000 in lost production and material waste.

The Hidden Cost of 4-20mA Loop Noise in Hydraulic Presses

First, we assumed the problem was mechanical—perhaps a worn pump or leaking valve. However, after thorough inspection, those components were fine. Then, we turned to the instrumentation. A 4-20mA loop is a current source, but long cables act as antennas for electromagnetic interference (EMI). Over time, this noise accumulates at the PLC input card, causing drift that mimics real pressure changes. Consequently, the PLC would command the press to cycle slower, thinking pressure was higher than actual. This means the root cause was not mechanical but electrical.

What Our PLC Didn’t Tell Us About EMI Noise Accumulation

During our investigation, we discovered that each cable run was over 100 meters long, significantly increasing the risk of interference. The hydraulic system’s critical nature meant we couldn’t afford false readings. Specifically, the noise was common-mode, affecting both signal wires equally. Traditional 4-20mA systems have poor common-mode rejection, especially over long distances. Therefore, the PLC saw a shifted signal that drifted with ambient electrical noise from nearby motors and VFDs.

How DR3702 Solved Our EMI-Induced Pressure Drift

After exploring various options—including shielded cables, signal isolators, and even wireless transmitters—we decided on the DR3702 digital pressure gauge. Its RS485 differential signaling rejects common-mode noise entirely. Additionally, the gauge offers both 4-20mA and RS485 outputs, providing flexibility. Installing the new sensor was straightforward; we simply replaced the existing gauge and ran a twisted-pair cable for RS485. Within days, our process stability improved dramatically.

15% Scrap Reduction and 10% OEE Gain: The DR3702 Impact

Scrap rates dropped by 15%, and overall equipment effectiveness (OEE) increased by over 10%. The reliability of our hydraulic press operations became much more predictable. Moreover, the LCD display with backlight and 5-digit readout allowed operators to see real-time pressure with high resolution. The nonlinear correction feature compensated for any sensor nonlinearity, ensuring accuracy across the full range.

Key Specifications

• Output signal: 4-20mA or RS485
• LCD display with backlight
• 5-digit display
• DC24V powered
• Multiple engineering unit display options
• Nonlinear correction
• Active or passive migration
• Durable housing for industrial environments

Closing Question

What’s the length of your longest 4-20mA cable run—and how much noise is it picking up? If you’re experiencing unexplained process variability, consider evaluating your signal integrity before assuming mechanical failure.

Tags: #RS485pressuretransmitter #4-20mApressuregauge #EMIresistantpressuresensor #digitalpressuregaugewithRS485 #DR3702