HM Digital Dual TDS Monitor (DM-3)

In-Line Dual TDS Monitor for Feed & Product Water

A single TDS reading after a filtration system tells you the output quality, but not whether the system is actually doing its job. The HM Digital Dual TDS Monitor (DM-3) reads feed (input) and product (output) water simultaneously, so you can see filtration effectiveness in real time.

Sold as one HM Digital DM-3 in-line monitor.

Key Features & Benefits

• Dual-probe in-line monitoring — displays TDS for feed and product water simultaneously.
• Shows real-time filtration effectiveness — compare input vs. output water quality at a glance.
• ±2% accuracy, factory pre-calibrated — calibrated with 342ppm NaCl solution before it ships.
• Backlit LCD with 3-minute auto-off — readable in low light, conserves the 2×AA batteries when idle.
• Nine fitting configurations available — 1/4in, 3/8in, and 1/2in feed/product line combinations.

Who Should Use the HM Digital DM-3

This fits growers and water-treatment setups running RO or DI filtration who want to monitor feed and product water TDS side by side, rather than checking each separately.

About the HM Digital DM-3

The DM-3 is an in-line dual TDS monitor built to compare feed and product water on RO/DI systems, factory pre-calibrated and available in nine fitting configurations.

Frequently Asked Questions

What does the DM-3 measure?

It measures Electrical Conductivity (EC) and Total Dissolved Solids (TDS) using dual probes, one on the feed (input) line and one on the product (output) line. That dual reading shows filtration effectiveness in real time.

How is the DM-3 calibrated?

It ships factory pre-calibrated using a 342ppm NaCl solution, with digital calibration capability if you need to recalibrate later. That factory calibration means it's ready to install and use out of the box.

What fitting sizes does the DM-3 come in?

It's available in nine fitting configurations, including combinations of 1/4in, 3/8in, and 1/2in for both the feed and product lines, plus a no-fittings base option. That range covers most common RO/DI plumbing setups.

How long does the battery last on the DM-3?

It runs on 2xAA batteries and automatically shuts off after 3 minutes of inactivity to conserve power. That auto-off feature extends battery life on a monitor left connected long-term.