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Water Level Controller with Reed Sensor

This is a way by which you can monitor the level of fluids like water in a tank. Based on data from the sensor you can control things like solenoids or motors as required or even turn on a buzzer, hooter or annunciator in a control panel. A simple Water Level Controller.


Look at the picture on the right, the float can be a Styrofoam type with a couple of ceramic magnets stuck inside. The float must move freely up and down a long plastic pipe of around 10 mm dia. If the fluid is not water but a solvent then design a non-soluble float or coat the float you made with something like an epoxy resin.

Water Level Controller

Then you need to assemble a small circuit within the long plastic pipe. Many reed relays with a chain of resistors in series has to be inserted in the pipe. The resistor and the glass reed relays should be in different levels of the pipe where you need an alarm or indication. Seal the pipe hermetically at both ends with epoxy resin after taking out a shielded cable of just 2 wires + 1 ground shield.

When the fluid level changes, the float moves up or down with it, when the float moves over a section of pipe where the reed relay is mounted, the magnets on the float make the reed operate and the resistance of the sensor changes.

The resistance is measured and the alarm can be operated as you like. The advantage of this arrangement is the electric circuit does not come in contact with the fluid, no sparking risk.

Reed Relay. It was invented by Dr. W. B. Ellwood at Bell Labs in 1936. Contacts are in a sealed glass tube filled with inert gas like in a bulb, so they do not corrode. It is faster than regular relays and as no spring is used it has a longer mechanical life. The two contacts are ferromagnetic blades plated with rhodium. When you take a magnet close by, the contacts touch each other. You can also put the reed in a coil, then when you energize the coil the reed operates. Used in telecommunication.OKI is one manufacturer of this type of component.

Design and Caution.

When you drive inductive loads you have to use RC snubbers, freewheeling diodes, varistors or zeners. when you drive lamps the cold current is high so use thermistors. The Reed relay is best used in telecom and instrumentation and avoided in power electronics. It can handle high RF frequency as the path of current is straight and footprint small.

Here is a Circuit to Build and Learn this Concepts – This can help make a Water level controller from sump to overhead tank. This can also be used in industrial fluid level control like oils and thick fluids. It may not work with highly viscous fluids or sticky mixes.

Fluid or Water Level with Reed Relays

“When you use the DMM or digital multimeter, try not to use it for high voltages and currents, use Solderman Talks 1702 external shunts and attenuators instead. If you try to measure 230V AC in the Ohms mode or in the Current mode with the probe in the current socket then you will see fumes in your DMM and a hole in your pocket !!”

– Solderman Talks 1702

Modbus-IDA – Distributed automation systems

Group of individuals and firms supporting and helping the implementation of Modbus communication protocol suite and the evolution to address architectures for distributed automation systems.

Modbus Communication Protocol Suite

Some Activities of the Modbus Organization are …to Encourage, support and evolve …

  • Participation in standards activities worldwide.
  • Leading the evolution of the Modbus protocol and its variants.
  • Modbus across a broad spectrum of physical layers and transmission media.
  • Conformance testing program to insure greater interoperability of Modbus devices.

Some Facts –

Modbus Protocol is a messaging structure developed by Modicon (Schneider Electric) in 1979. It is used to establish master-slave/client-server communication between intelligent devices. It is a de facto standard, truly open and the most widely used network protocol in the industrial manufacturing environment.

The semiconductor industry has implemented a Network Communication Standard and an Object Messaging Protocol using Modbus TCP/IP. This allows SEMI Sensor Bus compatible sensors to communicate with each other using Modbus TCP/IP.

Modbus mMint

The mMINT (Modbus Master INCOM Network Translator) Module is an Eaton accessory product that will provide communication between a Modbus RTU network and an INCOM network.

The mMINT module is a slave device on the Modbus network and as such requires a master that will exchange register objects with the mMINT module. 32 products can be connected to INCOM network port (246 unique addresses maximum).