Questions About Inline Monitors, Controllers, Aquaswitches:

Posted by 20 Mar, 2014 is the premier online distributor of Myron L Instruments. We make it easy to shop for your water quality testing instruments online. We understand that in order to make a buying decision you need more than just a recommendation or a product description. At you will find detailed information about every product, including demo videos and customer reviews.

Since the 1960s, Myron L products have led the industry in high quality, simple to operate conductivity and pH instrumentation for municipal, commercial and industrial water quality control, chemical concentration testing and process control. Today, Myron L meters are more convenient than ever to research and buy right here at We provide the background, insight, product imagery and specifications you need to make the right choice–all in one convenient online store. Have questions that aren’t answered in our FAQ section or on the blog? Ask an expert by filling out a short form and we’ll respond with an answer within 24 hours. At our mission is simple: Provide the best products with the best service, every day. We are proud to represent a quality product from a quality manufacturer!

My 750 Series II Monitor or Monitor/Controller display shows a 1, then a space, then a decimal point. What does this mean?
This is an over-range condition that can be fixed by performing an Electronic calibration of the circuit board. Please see directions in the Operations Manual or follow this brief review of Electronic Calibration. Hook up a Multi-Meter to the R+ and R- leads located at the top of the circuit board, switch the Multi-Meter to DC volts, push the Full Scale Push to Test button and read the DC voltage on the Multi-Meter. While pushing the Full Scale Push to Test button, adjust the CAL screw on the circuit board until the Multi-Meter reads 9.95-10.00 VDC. The display on the Myron L Monitor or Monitor/Controller should now read Full Scale.

How do I pick the correct range module for my Monitor or Monitor/Controller?
You must pick a range module that covers your 2/3 of your operating range. If you pick a range module that is too broad, then your accuracy will suffer or it will not show a number on the display. For example, if your operating range is 100-150 microsiemens, a range module of 0-200 microsiemens (-115) would be a good choice. A range module of 0-5,000 microsiemens (-123) would not be a good choice for this application.

Why does my displayed number fluctuate?
There is air or air bubbles around the sensor or the sensor is not properly installed. Tap on the sensor body to dislodge air bubbles or loosen securing nut to release trapped air. The sensor tip must be in the flow of water.

My device connected to the dry contact relay does not work and has no power. What do I do?
The Myron L dry contact relay does not draw power from the circuit board. You must supply the power to the relay to power your device.

Why is the display number on the Monitor or Monitor/Controller negative?
This is the offset that is being display and is caused when the sensor is not hooked up or is hooked up and sitting in air.

Why is the displayed number on the Monitor or Monitor/Controller half the reading than it should be?
This is caused when the 115/230 VAC switch is set to 230VAC when in fact it should be switched to 115 VAC.

Does the Aquaswitch I require any other device to help it switch banks?

Yes, the AquaSwitch I requires a Monitor/Controller in order to switch banks.

What is the recommended method to mount a Conductivity or Resistivity sensor?
The optimal method to mount the sensor is in the end of a tee with the water flowing directly into the tip of the sensor and flowing up and away at a 90 degree angle. Please see the 750 Series II Operations Manual for complete instructions.

I want to use my Monitor or Monitor/Controller for another application but the water quality is a totally different range. Can my existing unit be changed?
Our 750 Series II Conductivity/TDS and Resistivity Monitors and Monitor/Controllers can be “Re-Ranged” with a new range module to meet you changing needs. Simply un-plug the old range module and plug in the new range module into the circuit board. Refer to page 8 of the Operations Manual to see the Range Selection guide and to see if any minor modifications are necessary.

How can I tell what the model number of my Monitor or Monitor/Controller is?
The module number is circled on the transformer and printed on the back of the case.

Have other questions?  Try our literature database HERE, our video channel HERE, or use the handy Ask An Expert contact form at

Categories : Application Advice, Care and Maintenance, Product Updates, Technical Tips
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