HM-DIGITAL-DM-2

DM-2 HM Digital Commercial Inline Dual TDS Monitor

Name: DM-2 HM Digital Commercial Inline Dual TDS Monitor
Brand: HM Digital
SKU: HM-DIGITAL-DM-2
Price: 52.29 USD
Availability: OutOfStock

Out of Stock

Features & Specs

Package Qty: 1

Manufacturer: HM Digital

Manufacturer's Id: DM-2

UPC: 799705707115

Actual Size (in): 4 3/5 inches (height) x 2 3/5 inches (width) x 7/10 inch (depth)

Brand: HM Digital

Depth (in): 0.7 in

Fitting Size (in): 1/4 inch

Height (in): 4.6 in

Width (in): 2.6 in

Power Requirements: 2 x AA Batteries (included), Battery Life: Approximately 12 to 18 Months

Country of Origin: China

Fitting Type: Quick Connect

Instructions

The DM-2 is designed to be used with flowing water. Due to nature of mobile charged ions in electrical conductivity and flowing water, it is normal to experience discrepancies and fluctuations within 2% of the readings
Make sure the sensor is properly inserted into the fitting. Once the sensor has been inserted into the fitting, look through it. You should only see one metal probe
Always wait 10-20 seconds for more accurate readings. Rinse in de-ionized water or alcohol after prolonged use to ensure proper readings. Do not drop or submerge unit in water. Do not store unit in high temperature or direct sunlight
HM Digital monitors are factory-calibrated at 342ppm NaCl. Calibrate as close as possible to the test sample. Ensure accuracy by recalibrate your meter using a commercial standard solution at 25 degrees C (77 F); prior to usage and after prolonged usage
For drinking water, it is recommended to calibrate in a range of 90 ppm to 700 ppm. On the DM-2, calibration for both sensors is simultaneous. You need a tube/hose that is the same size as the fittings., a bucket or basin, and a pump
Step 1: Attach the IN and OUT sensors to the tubing that you will use for the calibration. It will be necessary to cut the tube in two places so that the solution will be running through both and so that the sensors are not too far apart from each other
Step 2: Configure the tube within a bucket or basin, using a pump so that the calibration solution will be cycled through the tube. In other words, the calibration solution needs to be flowing over both sensors to calibrate properly
Step 3: Turn on and measure calibration solution. If reading is not within 2% of solution
Step 4: Once the meter reads within 2% of the solution, gently release pressure on the screwdriver and remove from the trimmer pot. If the screwdriver is retracted abruptly, the reading may jump
Step 5: Turn the monitor off and on. Verify the readings for both sensors. If the readings are accurate with 2%, calibration is complete. If not, repeat the procedure

Downloads

User Guide

Product Details

The DM-2 is the perfect companion to any reverse osmosis or deionization system. You need to know the inlet and outlet TDS to truly know when to replace your membrane or resin. Simplify this process by installing the DM-2. Designed to be easy enough to install in residential applications, but built tough enough for industrial use, the DM-2 is a highly accurate TDS meter with a very long two year battery life, and large easy to read LCD.

Frequently Asked Questions

What does the HM Digital DM-2 Commercial Inline Dual TDS Monitor actually measure?

The HM Digital DM-2 is a dual-display TDS (Total Dissolved Solids) monitor designed to simultaneously measure the TDS levels of both your incoming (pre-filter) and outgoing (post-filter) water in parts per million (ppm). This allows you to instantly verify the performance and rejection rate of your reverse osmosis or water filtration system. It measures a range of 0–9999 ppm with an accuracy of +/- 2%, making it ideal for commercial RO systems, drinking water applications, and hydroponics.

How is the HM Digital DM-2 installed on my RO system?

The DM-2 is an inline monitor that installs directly onto your water filtration system using two dual in/out probes that connect to standard 1/4" quick-connect tubing. One probe is placed on the feed water line (before filtration) and the other on the product water line (after the RO membrane). The unit is powered by a single 3V lithium battery (included) and features a push-button operation to toggle between the IN and OUT readings on the LCD display.

Does the HM Digital DM-2 require calibration or filter replacement?

Unlike filtration cartridges, the DM-2 is a monitoring device and does not have a micron rating, NSF/ANSI filtration certification, or a gallon-based replacement cycle. It is factory-calibrated to a 342 ppm NaCl solution and typically does not require user recalibration under normal use. The only routine maintenance is replacing the 3V lithium battery, which generally lasts around 1 year (approximately 2,000 hours of use) depending on frequency of readings.

How do I know when my RO membrane needs replacement using the DM-2?

The DM-2 makes membrane monitoring simple. Calculate your rejection rate by comparing the IN (feed) ppm to the OUT (product) ppm. A healthy RO membrane should reject 90–98% of dissolved solids. For example, if your feed water reads 300 ppm and your product water reads 15 ppm, your rejection rate is 95%. When the rejection rate drops below 80–85%, it's typically time to replace your RO membrane. The DM-2's dual simultaneous readings eliminate the guesswork of single-line TDS meters.

What are the operating specifications and limits of the DM-2?

The HM Digital DM-2 operates within a temperature range of 0–80°C (32–176°F) and is designed for cold water lines only — it should not be installed on hot water applications. It features automatic temperature compensation (ATC) from 1–50°C for accurate readings regardless of water temperature, and uses a conversion factor of 0.5 (NaCl). The probes are constructed with a maximum working pressure of 100 psi, making it compatible with standard residential and light commercial RO systems.

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