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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.

Description.

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 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).

Two Stage Sequential Timer Docs

The circuit is a two stage sequential timer with auto reset. It can turn a Solenoid On/Off after a Sequence of delays that are preset. This is also a basic example of timer usage in automation.

Design Documents

Source Files Orcad Format

All Timers are 1 – 30 Secs Analog with Presets to adjust with a screwdriver. The Switch, Solenoids and Power supply has to be via terminal blocks or plug-jacks. The PCB may be upto six Square Inches for standard DIP components but with SMD it may be smaller.

Block Diagram :

Sequential Timer Specs

The PCB has to be tested to conform with the circuit, this has to be Meticulous. The Circuit is for the Battery and Solenoid Specified and will have to be modified if battery and solenoid are different. D1 to D4 can be replaced by a 300V 3A Bridge Rectifier Module. F1 fuse could be 2A – 3A Slow Blow depends on Solenoid inrush current. Presets can be with some graduations if possible for ease of adjustments. LED resistors can be a bit lower if more brightness is required.

Four Channel Temperature Alarm Docs

The temperature in a pipe is monitored with four RTD Pt-100 Sensors, The type of probe could be Extruder RTD probes with Bayonet or Compression Fitting, Get it from Omega. To keep costs low you can choose small thin film RTD sensors, they will be fast but on rough usage may break.

Design Documents

Source Files Orcad Format

The time taken to measure the temperature at the 4 points will be less than 4 seconds. An optional display of the measured temperature as shown above can be avoided by using a DMM to adjust the setpoint.

The Analog Timer Module can be set from 0- 30 minutes. If out-a remains high even after set time a out-b alarm goes on to sound a buzzer and flash a LED light.

Block Diagram :


Four Channel Temperature Alarm

It all started with a email from a client like this ……….

“I am looking at an idea for a circuit design; The idea is to sense a temp of 130 degrees and then light an LED and start a timer delay. The delay would be 3 min, after the delay if the temp is still above 130 sound alarm.

With the LED I would like to drive a counter display to show how many times the temp was sensed. I would like powered by 120vac and a 9 volt battery backup for counter circuit. If you can assist please let me know.”