HM Digital SM-1 Single Inline TDS Meter – RO & DI Water Monitor

The HM Digital SM-1 Single Inline TDS Meter provides a simple, permanent way to monitor the TDS level of a single water line.

It is particularly useful for Reverse Osmosis (RO) and deionisation (DI) systems, allowing you to check the TDS of the filtered product water at the press of a button without collecting a water sample or using a handheld meter.

The SM-1 installs directly into 1/4" tubing using the supplied quick-connect T-fitting and provides an easy-to-read digital TDS measurement whenever required.

Ideal for Monitoring RO Product Water

The SM-1 is normally installed on the filtered water outlet of an RO system.

Once installed, simply press the power button to see the current TDS reading of the water passing through the line.

Monitoring this reading over time can help identify changes in RO or DI system performance.

For example, if your RO water normally measures around 10 ppm but gradually increases to 20, 30 or 40 ppm under similar feed-water conditions, this may indicate that the membrane's performance should be investigated.

Want to measure both incoming and filtered water?
Consider the HM Digital DM-1 Dual Inline TDS Meter, which monitors both feed and product water and makes calculating RO membrane rejection much easier.

Features

• Permanently installed inline TDS monitor
• Measures TDS from one water line
• Ideal for RO and DI product-water monitoring
• Easy-to-read digital display
• Measurement range up to 9990 ppm
• ±2% accuracy
• Automatic Temperature Compensation (ATC)
• Factory calibrated at 342 ppm NaCl
• Can be recalibrated if required
• Automatic shut-off after approximately 10 minutes
• Battery powered – no mains power required
• Includes 1/4" quick-connect T-fitting
• Compact and easy to install

HM Digital states that the SM-1 is supplied with one 1/4" T-fitting and is factory calibrated using a 342 ppm NaCl solution. hmdigital.com

Specifications

Specifications are consistent with HM Digital's current product catalogue. hmdigital.com

Suitable For

• Reverse Osmosis systems
• RO/DI systems
• Deionised water systems
• Drinking water RO systems
• Aquarium RO/DI systems
• Hydroponics
• Water purification equipment
• Water coolers and dispensers

Easy Installation

The supplied sensor fitting installs directly into a 1/4" water line.

For an RO system, we generally recommend installing the SM-1 on the RO product-water line after the membrane.

Once installed:

1. Press the ON/OFF button.
2. Allow the reading to stabilise.
3. Read the TDS directly from the digital display.
4. The meter automatically switches off after approximately 10 minutes to conserve battery life.

HM Digital also notes that the sensor can be installed in different positions depending on the application, although filtered/product water is the typical installation point. Device Report

What Does TDS Mean?

TDS – Total Dissolved Solids – is a measurement of dissolved ionic material in water and is displayed in parts per million (ppm).

An RO membrane removes a large proportion of these dissolved substances, so monitoring product-water TDS provides a useful indication of changes in membrane performance.

Important

A TDS meter does not identify individual contaminants and does not determine whether water is microbiologically safe.

It is also important to understand that conventional sediment and activated carbon filters may remove contaminants without significantly changing TDS. The SM-1 is therefore particularly useful for monitoring technologies such as Reverse Osmosis and deionisation, where changes in dissolved solids are relevant.

What's Included

• HM Digital SM-1 Single Inline TDS Monitor
• 1 × inline TDS sensor
• 1 × 1/4" quick-connect T-fitting
• Batteries
• Operating instructions

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SM-1 vs DM-1

Choose the SM-1 if you simply want to monitor one water line.

Choose the DM-1 if you want to compare the feed water and RO product water from the same permanently installed meter.