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HM Digital DM-1 In-Line Dual TDS Monitor, 0-9990 ppm Range, +/- 2% Readout Accuracy,Blue & White

4.6 4.6 out of 5 stars 2,516 ratings
$24.48 with 6 percent savings
Typical price: $25.99

This is determined using the 90-day median price paid by customers for the product on Amazon. We exclude prices paid by customers for the product during a limited time deal.
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Purchase options and add-ons

Brand HM Digital
Material Plastic
Number of Batteries 2 LR44 batteries required. (included)

About this item

  • plastic
  • Imported
  • 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 In-Line Dual TDS Meter displays TDS levels of the feed water and product water with in and out electrode probes
  • This TDS Monitor is highly efficient and accurate due to its advanced microprocessor technology
  • Highly efficient and accurate due to its advanced microprocessor technology
  • Auto-Off function conserves battery power. The unit shuts off automatically after 10 minutes of non-use
  • Installs quickly and easily
› See more product details

Customer ratings by feature

Easy to use
4.5 4.5
Easy to read
4.3 4.3
Accuracy
4.3 4.3
Value for money
4.0 4.0
See all reviews
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Product Warranty: For warranty information about this product, please click here [PDF ]

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HM Digital DM-1 In-Line Dual TDS Monitor, 0-9990 ppm Range, +/- 2% Readout Accuracy,Blue & White

HM Digital DM-1 In-Line Dual TDS Monitor, 0-9990 ppm Range, +/- 2% Readout Accuracy,Blue & White

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Product Description

Product Description

Product Description: How Pure is Your Water? HM Digital's DM-1 is a dual inline monitor that measures TDS from 0 to 9990 ppm. It includes batteries, two sensors and two 1/4" quick-connect T-fittings. The DM-1 is an easy and convenient method of determining TDS levels for water filtration/purification systems such as reverse osmosis (RO), deionization (DI) and more. It's very useful for coolers or under-the-sink systems. For any type of system that removes TDS, you can install the 'IN' sensor on your tap water (before the system) and the 'OUT' sensor on your product water (after your filtration system) to determine the filter/membrane's effective operating (rejection) rate.

From the Manufacturer

In-Line Dual TDS Monitor.

Customer reviews

4.6 out of 5 stars
4.6 out of 5
2,516 global ratings

Customers say

Customers like the performance, ease of installation, and accuracy of the dimensional measurement caliper. For example, they mention it works well, easy to install, and accurate. That said, opinions are mixed on readability, quality, and size.

AI-generated from the text of customer reviews

212 customers mention192 positive20 negative

Customers are satisfied with the performance of the dimensional measurement caliper. They mention that it works well, is accurate, and provides instant results. Some say that the leads are about 24-inches long and a bit short. Overall, most are happy with the product's performance and recommend it to others.

"works well" Read more

"Easy, affordable,good instructions and works perfectly. All there is to say." Read more

"2 cuts and 2 minutes to install. Works well just a bit hard to read. Worth every penny of $25." Read more

"...The meter output matches handheld conductivity and its inexpensive...." Read more

132 customers mention132 positive0 negative

Customers find the installation of the dimensional measurement caliper to be easy. They mention that it's simple to install, use, and adjust. They also appreciate the convenience and accuracy of the product.

"Easy, affordable,good instructions and works perfectly. All there is to say." Read more

"Easy to install after my inline meter died after years of use! Working just fine !" Read more

"...Easy to install and the unit will turn off by itself after a few minutes if you don't which saves the battery life." Read more

"Easy to install and use. Gives great piece of mind" Read more

63 customers mention50 positive13 negative

Customers like the accuracy of the dimensional measurement caliper. They mention that it's easy to install, gives accurate input PPM and output PPM, and that the readings are nearly identical.

"This has been super useful and very accurate so far. Get a 3 prong unit if you use a dual setup but the will be fine for most" Read more

"I feel that this is VERY accurate. I purchased a reverse osmosis system and installed both the meter and the system at the same time...." Read more

"...Pretty accurate, as you can see in the pics. Spliced right in to my existing 1/4" line." Read more

"...The readings seemed reasonably correct. But then I put the meter on my reverse osmosis rain water (sistern) filtration system...." Read more

33 customers mention33 positive0 negative

Customers appreciate the value of the dimensional measurement caliper. They say it's an economical meter that saves them money on maintenance. Some customers also mention that it'll track their other handheld meter quite well. Overall, most are happy with their purchase and recommend it to others.

"Easy, affordable,good instructions and works perfectly. All there is to say." Read more

"...to install. Works well just a bit hard to read. Worth every penny of $25." Read more

"...The meter output matches handheld conductivity and its inexpensive...." Read more

"...TESTOR... two sensors..LCD readout...miniature sized ..at a reasonable price....clicked ..that Amazon TO CART...Prime...Thu..arrived..." Read more

45 customers mention24 positive21 negative

Customers are mixed about the quality of the dimensional measurement caliper. Some mention that it's a great product, well constructed, and reliable, while others say that it is fragile and defective. The LCD screens are also of poor quality.

"...The product concept is great and it's easy to switch from source water to RO." Read more

"These work. They are also made in a country that is not known for quality products. This one is a back up as the one in use often says "Err"...." Read more

"...purification system 18 months ago...extremely delighted..pleased with the pure water...routed 2 ..1/4 inch pure water lines ...1 to our Sam Sung..." Read more

"I've had to purchase this multiple times due to the lcd screens quality...." Read more

32 customers mention19 positive13 negative

Customers are mixed about the readability of the dimensional measurement caliper. Some mention that the readings are easy to read and appear to be accurate, while others say that the meter fails to read the reading of the water running in and out.

"...readings with the calibrating solutions and especially with reproducible readings and fantastic agreement between the two probes...." Read more

"This was easy to install however not easy to read, would be easier if it would have a light for the screen. This is way too dark for me...." Read more

"...The display is easy to read and it turns off by itself. I personally like to stay in the habit of manually turning off equipment when not needed...." Read more

"The product is very easy to use and easy to read. There were no bad surprises when I used it and easy to understand instructions...." Read more

15 customers mention8 positive7 negative

Customers have mixed opinions about the size of the dimensional measurement caliper. Some find it small and compact, while others say it's fragile and the leads are too short. Some say the product works and is not very expensive.

"...360 tds in and 0 out tds. This is a nice, compact and complete solution for TDS and water filtration." Read more

"Overall, seems okay. Leads are about 24-inches long and a bit short. Display is tiny." Read more

"it measures TDS just fine, but I found out it cannot detect dissolved sugar in water (Maple sap) so for my Maple Syrup RO rig this does me no good..." Read more

"...Result: 500 - 600 TDSThese are absolute garbage for taking a real measurements...." Read more

8 customers mention4 positive4 negative

Customers are mixed about the leakage of the dimensional measurement caliper. Some mention that it's still working well, while others say that there was some leaking. Some customers also mention that the batteries were leaking and were dead the day after installing it.

"Works as advertised. No leaks, allows me to check the TDS for incoming and outgoing water, and I don't feel the pressing need to replace the RO..." Read more

"One of the two 3-way connectors leaks so only my filtered water will be measured (which is fine). I attempted to recut tube end with no success...." Read more

"...I keep a little flashlight in there with it. Simple installation, no leaks." Read more

"...it has been that the original button cell batteries (2 LR44s) started to leak a year or two ago...." Read more

Cheap and easy.
5 Stars
Cheap and easy.
2 cuts and 2 minutes to install. Works well just a bit hard to read. Worth every penny of $25.
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Top reviews from the United States

David Jung
5.0 out of 5 stars easy to install
Reviewed in the United States on April 16, 2024
Verified Purchase
works well
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Amazon Customer
5.0 out of 5 stars Cheap and easy.
Reviewed in the United States on April 6, 2024
Verified Purchase
2 cuts and 2 minutes to install.
Works well just a bit hard to read.
Worth every penny of $25.
Customer image
Amazon Customer
5.0 out of 5 stars Cheap and easy.
Reviewed in the United States on April 6, 2024
2 cuts and 2 minutes to install.
Works well just a bit hard to read.
Worth every penny of $25.
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Customer imageCustomer image
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solitary man
5.0 out of 5 stars Awesome
Reviewed in the United States on February 22, 2024
Verified Purchase
Easy, affordable,good instructions and works perfectly. All there is to say.
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mbon
4.0 out of 5 stars Useful but difficult to read
Reviewed in the United States on December 16, 2023
Verified Purchase
This meter functions fairly well. If the two sensors don't have enough water around them in fitting they read low, so they need careful placement in T fittings. The meter output matches handheld conductivity and its inexpensive. My main issue is the low contrast LCD display that requires direct view and more than ambient light. The product concept is great and it's easy to switch from source water to RO.
3 people found this helpful
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OKCSteve1
5.0 out of 5 stars So far great
Reviewed in the United States on February 5, 2024
Verified Purchase
This has been super useful and very accurate so far. Get a 3 prong unit if you use a dual setup but the will be fine for most
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DonS
5.0 out of 5 stars It works
Reviewed in the United States on January 8, 2024
Verified Purchase
Easy to install after my inline meter died after years of use! Working just fine !
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Guillaume Delmas
5.0 out of 5 stars I love it
Reviewed in the United States on November 6, 2023
Verified Purchase
So easy to monitor PPM of your RO and monitor the efficacy of your membrane with the 2 probes. Easy to install and the unit will turn off by itself after a few minutes if you don't which saves the battery life.
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Michael Marsden
5.0 out of 5 stars Works great
Reviewed in the United States on November 28, 2023
Verified Purchase
Easy to install and use. Gives great piece of mind
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Top reviews from other countries

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Bernardo Palomares torres
5.0 out of 5 stars Excelente producto
Reviewed in Mexico on July 17, 2023
Verified Purchase
Todo muy bien .....
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rodrique jean michel
5.0 out of 5 stars Super produit
Reviewed in France on March 10, 2024
Verified Purchase
Très bien je recommande
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Vasco
5.0 out of 5 stars Tds
Reviewed in Germany on December 13, 2023
Verified Purchase
Perfect fit for reverse osmosis
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Suneetha Raja
3.0 out of 5 stars Does what it says
Reviewed in Sweden on July 18, 2022
Verified Purchase
Does what it says on the box.
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Consumer Report
5.0 out of 5 stars Easy to install and accurate
Reviewed in Canada on July 3, 2020
Verified Purchase
Bought this unit for my shrimp tanks. I have dual membranes so I placed the sensors after each membrane. It works great and I can see how the membranes are reducing my tds from 156 to 1 so very accurate a great time saver. To install was very simple just clip the line and push fitting where you want it a great item and good buy. Only suggestion I would have for mfg would be to have a clip on option as opposed to sticker on back to adhere to your ro unit.
2 people found this helpful
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