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HM Digital DM-1 In-Line Dual TDS Monitor for In / Out Water Lines

Price $41.99 List Price Price $59.99 Save 30%
Availability: Discontinued
The DM-1 helps you to measure the tap water coming in vs. the purified water going out of your water filtration system at any time. The inline Dual TDS Meter displays TDS levels of the feed water and product water with in & out electrode probes. This TDS Monitor is highly efficient and accurate due to its advanced microprocessor technology. The Dual TDS Monitor has an auto-off function that conserves battery power. The unit shuts off automatically after 10 minutes of non-use. Dual Range: 0-9990 ppm (from 0--999 ppm the resolution is 1 ppm; from 1000 to 9990 ppm, the resolution is 10 ppm, indicated by a blinking 'x10' image). The DM-1 TDS monitor is factory calibrated with a 342 ppm NaCl solution and can be recalibrated with a mini-screwdriver. The DM-1 monitor comes equipped with Mur-lok Quick-Connect T-fittings. The DM1 Dual Total Dissolved Solids Monitor installs quickly and easily.
Package Qty1
Used In BrandsHM Digital
Manufacturer's IdDM-1
Actual Size (in)3 inches (height) x 8/10 inch (width) x 1 9/10 inches (depth)
Actual Size (cm)7.62 x 2.032 x 4.826
Fitting Size (inches)1/4 inch
Power RequirementsPower Source: 2 x 1.5V button cell batteries (included), Battery Life: Approximately 1000 hours of continuous use
Country of ManufactureChina
Warranty Guarantee1-Year Limited Warranty

Reduced Contaminants

The HM-DIGITAL-DM-1 is comparable with the following part numbers


User Guide


  1. The DM-1 is designed to be used with flowing water. It is normal to for discrepancies and fluctuations within 2% of the readings. Make sure sensor is properly inserted into fitting (once inserted, look through; only one metal probe should be visible)
  2. Always wait 10-20 seconds for more accurate readings. Rinse in de-ionized water or alcohol after prolonged use to ensure proper readings. The base of the DM-1 is not waterproof. Do not store unit in high temperature or direct sunlight
  3. HM Digital monitors are factory-calibrated at 342ppm NaCl and designed to stay consistent. However, you may need to recalibrate your meter. TDS meters are most accurate when calibrated as close as possible to the sample to be tested
  4. Calibrate at 25 deg C (77 deg F). To ensure accuracy, recalibrate your meter using a commercial standard solution. This should be done prior to usage and after prolonged usage. For drinking water a range of 90 ppm to 700 ppm is recommended
  5. For the DM-1, calibration is done for both sensors simultaneously. You will need the following: Calibration solution. A tube/hose that is the same size as the fittings. A bucket or basin. A pump
  6. Step 1: Attach the IN and OUT sensors to the tubing you will use for the calibration. It will be necessary to cut the tube in two places so that the same solution will be running through both sensors and so that they are not too far apart from each other
  7. 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
  8. Step 3: Turn on and measure calibration solution. If reading is not within 2% of solution, use a mini screwdriver in the trimmer pot (small hole on rear of the monitor) to adjust. Clockwise = up; counterclockwise = down. Note: Trimmer pot is sensitive!
  9. 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
  10. 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