DR3702 RS485 Pressure Transmitter: Solving 4-20mA Loop EMI and Signal Drift

$60,000 in Scrap: How EMI Masqueraded as Sensor Failure

Last month, our hydraulic press began cycling slower than expected. The gauge showed normal pressure, yet every part was out of specification. Consequently, we faced significant downtime and scrap material, costing us an estimated $60,000 over the past year. Initially, we suspected genuine sensor failure, but the root cause turned out to be more subtle.

What SCADA Didn’t Tell Us About Our Pressure Drift

A 4-20mA loop is essentially a current source, but long cables act like antennas, making them susceptible to electromagnetic interference (EMI). Specifically, this EMI noise couples into the signal line, causing drift at the PLC input card. As a result, the PLC interprets this drift as a change in pressure, leading to inaccurate readings and poor process control. In our case, the drift was intermittent, making diagnosis challenging. However, by tracing the signal from the PLC input card, we observed erratic behavior that pointed to EMI rather than sensor degradation.

How DR3702 Solved Our EMI-Induced Measurement Errors

To resolve the issue, we switched from a 4-20mA pressure gauge to an RS485 pressure transmitter, specifically the DR3702 model. The DR3702 uses differential signaling, which inherently rejects common-mode noise, making it highly EMI resistant. Additionally, it offers both 4-20mA and RS485 output options, providing flexibility for future upgrades. The installation was straightforward, and we immediately noticed stable readings. Furthermore, the DR3702’s nonlinear correction feature compensated for any sensor nonlinearity, ensuring accuracy across the full pressure range.

Why $60,000 in Savings Was Just the Beginning?

After implementing the DR3702, our pressure readings became consistent and reliable. We eliminated the need for frequent recalibration and reduced scrap material by 90%. Consequently, we saved approximately $60,000 in operational costs in the first year alone. Moreover, the improved process control led to higher product quality and reduced downtime. The DR3702’s durable housing ensures long-term performance in harsh industrial environments, making it a cost-effective solution for EMI-prone applications.

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

Is your pressure drift actually sensor failure, or just EMI on the signal line? The DR3702’s EMI-resistant RS485 output could save your facility thousands in scrap and downtime. Consider evaluating your measurement loops for EMI susceptibility—it might be the most profitable diagnostic you perform this year.

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