Description
Monitor water quality at two points in your filtration system with the HM Digital DM-3 Commercial Dual Inline EC/TDS Monitor.
The DM-3 uses two inline sensors to measure both electrical conductivity (EC) and total dissolved solids (TDS). It is ideal for comparing untreated and treated water, monitoring RO performance, or checking the water quality between two deionisation stages and at the final outlet.
Its large backlit display, high low-range resolution and individually calibrated sensor lines make the DM-3 particularly well suited to reverse osmosis, deionisation and spot-free rinse systems.
Monitor Two Water Lines
The two sensors can be installed at different points within a water-treatment system.
Common installations include:
- Feed water and RO product water
- Feed water and final DI water
- Between two DI cartridges and after the final DI cartridge
- Before and after a demineralisation system
- Incoming water and final treated-water outlet
For a two-stage DI system, Line 1 can be positioned between the two DI cartridges and Line 2 after the final cartridge. This allows the first cartridge to be monitored for breakthrough while the second cartridge continues to polish the final water.
Key Features
- Measures both EC and TDS
- Dual inline sensors for monitoring two water lines
- Large, easy-to-read backlit LCD display
- High resolution down to 0.1 ppm below 100 ppm
- Stated accuracy of ±2%
- Independent digital calibration for Line 1 and Line 2
- Factory calibrated to a 342 ppm NaCl solution
- Diagnostic error messages
- Long 1.2 metre shielded sensor cables
- Stronger water-resistant commercial housing
- Adjustable mounting bracket
- Battery powered—no mains power connection required
- Two AA batteries included
Ideal Applications
The HM Digital DM-3 is suitable for:
- Reverse osmosis systems
- Deionised and demineralised water systems
- Mixed-bed DI cartridge monitoring
- Spot-free vehicle and aircraft rinse systems
- Window-cleaning water systems
- Commercial and industrial water treatment
- Aquariums
- Hydroponics
- Drinking-water filtration systems
- Laboratory and process-water monitoring
Why Monitor TDS?
TDS is an indication of the total concentration of dissolved ions in the water. Monitoring TDS helps show whether an RO membrane or deionising resin is continuing to remove dissolved minerals effectively.
A rising outlet reading can indicate that:
- An RO membrane is losing rejection performance
- A DI cartridge is approaching exhaustion
- Treated-water quality is beginning to deteriorate
- A cartridge or resin stage may require servicing
The DM-3 provides an immediate digital reading without needing to collect and test a separate water sample.
Why Choose the DM-3?
Compared with a basic inline TDS meter, the DM-3 offers:
- Both EC and TDS measurement
- Higher resolution for low-TDS DI water
- A larger backlit display
- Longer shielded sensor cables
- Separate digital calibration for each sensor
- A more robust water-resistant housing
- Diagnostic messaging
- A flexible mounting bracket
These features make it an excellent choice for commercial RO and DI systems where treated-water quality must be checked accurately and regularly.
Technical Specifications
Model: HM Digital DM-3
Measurement: Dual-line EC and TDS
TDS range:
0–5,000 ppm
0–5.00 ppt
EC range:
0–9,999 µS
0–9.99 mS
TDS resolution:
- 0.1 ppm from 0–99.9 ppm
- 1 ppm from 100–999 ppm
- 10 ppm from 1,000–5,000 ppm
- 0.01 ppt from 0–5.00 ppt
EC resolution:
- 0.1 µS from 0–99.9 µS
- 1 µS from 100–999 µS
- 10 µS from 1,000–9,990 µS
- 0.01 mS from 0–9.99 mS
Accuracy: ±2% of reading
TDS conversion factor: NaCl, approximately 0.5
Temperature compensation: Automatic, 0–60°C
Sensors: Two inline sensors designed for compatible 1/4-inch quick-connect fittings
Sensor cable length: 1.2 metres each
Calibration: Individually adjustable digital calibration for each line
Factory calibration: 342 ppm NaCl
Power supply: Two AA batteries, included
Monitor dimensions: Approximately 116 × 70 × 19 mm
Weight: Approximately 225 g
Housing: Water-resistant; not waterproof
Installation
The DM-3 is normally installed with:
- Line 1 connected to the feed water or an intermediate treatment point
- Line 2 connected to the final treated-water outlet
The sensor pins must be installed in the correct orientation across the direction of water flow.
For systems using larger pipework, the 1/4-inch sensors can be installed in a suitable flowing sample line or compatible sensor fitting without reducing the entire main water line to 1/4 inch.
Professional installation is recommended where the meter is being added to commercial or high-flow equipment.
Important Information
The DM-3 monitor housing is water-resistant but not waterproof. Install the display in a dry, protected location away from direct hose spray, weather exposure or possible submersion.
TDS and EC readings indicate the overall level of dissolved ions in the water. The DM-3 does not separately identify individual contaminants and does not directly measure hardness, pH, chlorine or microbiological water quality.