Understanding the growth of new technologies and keeping in mind of giving an added value to its existing product eStorm-L1, Embien launched an Android app named “DAQ Suite”. With experience in developing Android app for many segments such as IoT, healthcare, automotive etc we have developed “DAQ Suite” for enhancing user experience in multiple industrial applications such as remote control, remote data acquisition/logging, etc.

This blog is the sequel of the blog “eStorm-L1 as GSM based remote switch” demonstrating the relay control and sensor monitor via an Android app. The following video shows the remote monitoring and control application typically applicable in industrial domain and many other verticals. The demo is setup using the GSM based remote switch and android application controlling the device through SMS command.

For the demo purpose we have connected two LED’s and two switches for demonstrating the relay control and sensor monitor functionality respectively. In the real time application, the LED could actually be a relay with suitable external DC supply for coil excitation and switch could be a sensor/transducer output preferably a digital high/low signal or even a pulse type output. The device stores all the configuration settings corresponding to the user, IO, etc in the EEPROM and hence preserved even on power cycling. Also the device has an option to erase the memory on site and start the user settings from the initial factory default.

The DAQ Suite android app includes the following menu options

  1. Device type selection setting – To select the type of the device need to be monitored or controlled. Available device will be listed in the Device model list box.
  2. User settings – To set the user details such as name, phone number, password, device description, and phone number to be taken for call actions etc.
  3. Relay settings – To set the on duration, ON/OFF delay etc. For multiple relays, the name of the device attached to the relay can be set.
  4. Update settings – To set the update interval for how much time interval the user need to receive the SMS about the current status of the relay and digital input. Many options can be chosen from the list view such as on change, periodic, both and none.
  5. Call actions settings – To set the action to be done on the relay upon calling the device. Either the relay can be switched ON/OFF.

The main screen of the DAQ suite includes the status of the SMS command being sent and time information of the last received/sent SMS. The control switch to toggle the relay and the status LED of the digital inputs is also included in the main screen.

Upon every operation, a SMS will be sent to the device with the predefined command set and the respective status of the digital inputs and relay will be displayed on the main screen based on the acknowledge SMS from the device.

About Embien: Primary focus of Embien technologies lies in the Industrial Automation segment. We have a rich experience in working on industrial automation and control systems with customers across geographies to enable their factories and assembly lines run efficiently. Our team have developed protocol stacks for various industrial protocols and enabled them in customer devices. We have created various Human Machine Interfaces (HMI) systems to make easier the interface with the machine. Our Machine to Machine (M2M) service offering includes developing system capable of remote monitoring and controlling of machines, PLC’s, etc.

eStorm-L1 is a commercial off the shelf product from Embien. Loaded with many features, it is mainly crafted to support quick realization of customer requirements. eStorm-L1 has been currently deployed across industries for various functional applications.

This blog captures one of the most popular applications of eStorm-L1 as a GSM Remote Control Switch. Being based on our proven and reliable platform, the GSM remote switch brings to the industry a low cost solution and help reducing the man power. With just a SMS command to the device, multiple loads can be switched on and off. It also supports acquiring the current status of analog /digital sensors attached to it. Apart from industry applications, this remote switch can also be used for home automation purposes.

eStorm L1 – Device Information

eStorm-L1 based GSM remote control switch is a remote monitor and control device equipped with GSM connectivity and external digital IO interfaces.

Powerful MCU: The device is powered by industrial grade ARM Cortex M0+ micro-controller. It holds rich IO interface supporting multiple digital inputs and relay control outputs. The core can run at 48 MHz that is quite powerful for remote control and monitor application.

Digital Inputs and outputs: The device supports up to 4 digital inputs mainly to acquire the data from the sensor/transducers. There are option for up to 8 digital outputs in relay mode and 4 digital outputs in digital switch mode. Digital switch mode supports direct control of the load connected across the terminals whereas the relay mode supports the external relay control which controls the load connected it.

GSM Communication: The device includes dual band GSM modem with on board antenna and SIM card holder. The device supports standard 6-pin SIM card with 1.8V and 3V operating voltage.

Storage: EEPROM available in the device supports storing configurations and user account details such as user name, phone number, password etc.

Field upgrade: USB device and configuration switch is provided for field upgrade. Connecting to the PC/Laptop with the provided application and firmware will be sufficient to do the upgrade task.

Enclosure: The device is carefully designed and enclosed inside an ABC plastic enclosure to sustain under rugged industrial environment. It can be mounted on the wall through the protruded flanges in the sides of the enclosure lid.

Remote Control Switch – Operation

Device requires a valid SIM card to be inserted in the SIM card holder. User should carefully connect the load / sensors to the respective terminals. Load connected to eStorm-L1 can be controlled remotely by just sending a SMS command or a missed call for relay control. There are options for configuring one admin and up to 10 users. Only the admin has rights to add, delete the user accounts etc. Password and phone number should be valid to control the device.

Configuring the device is very simple. Just a missed call to the device will provide the administrator, a user name and password through SMS. This user name and password should be added in all the commands for valid operation and the same can be changed by the admin through SMS command. Following are the command groups and available commands that are supported by the device for remote switch application.

  1. Relay commands
    1. Group switch on/off relays
    2. Individual switch on/off relays
    3. Setting ON/OFF delay
    4. Setting ON duration
    5. Setting Relay status update option/period
    6. Setting missed call control action
  2. Inputs commands
    1. Group of inputs enable/disable
    2. Particular input enable/disable
    3. Setting ON/OFF de-bounce
    4. Setting input status update type and period
  3. Admin commands
    1. Add user
    2. Delete user
    3. Change password
    4. Change user phone number
    5. Getting user list
  4. Query commands
    1. Query device information
    2. Current relay and inputs settings
    3. Current status of inputs and relays
    4. Device network signal strength
  5. Help commands
    1. Missed call action command format
    2. Relay command format
    3. Input command format
    4. Admin command format
    5. Query command format

For all the above command types there are shortcut commands which supports easy and quick control actions for the user handling the device. Except the admin commands all the users have rights to use the commands providing a better hierarchy in control.

Following figure depicts example SMS command sent to the device and response received from the device respectively.

Example 1: Consider all relays are in off state. Issuing a command with user name and password to switch on relays connected to digital outputs 1, 3, 5, 7 at a time. The response confirmation message from the device will describe the list of relays in ON state i.e. 1, 3, 5, and 7 and the list of relays in OFF state i.e. 2, 4, 6, and 8.

Relay On command

GSM Relay On command

Example 2: Consider the relays 1, 4, 5, 8, inputs 1, 4 is ON and relay 2, 3, 6, 7, inputs 2, 3 is OFF. To get relay and input status information’s, sending query command to the device. The relay and inputs status will be sent by the device as shown in the figure upon the SMS command reception.

Status Query Command

GSM Switch Query Command

Applications of the GSM Controller

GSM based remote switch applications are generally numerous and with Embien’s device designed specifically for operating in -40 to 80 degrees, the net get even wider. Some of them include the remote control of industrial lighting, exhaust fans, engine/machine pre-heaters, cabin heaters, water well pumps, single phase/ 3-phase irrigation systems, power cycle and reboot of remote servers, routers and computers, HVAC – heating and air conditioning in holiday homes, aviation engine heaters, pumping stations, etc.

About Embien: Primary focus of Embien technologies lies in the Industrial Automation segment. We have a rich experience in working on industrial automation and control systems with customers across geographies to enable their factories and assembly lines run efficiently. Our team have developed protocol stacks for various industrial protocols and enabled them in customer devices. We have created various Human Machine Interfaces (HMI) systems to make easier the interface with the machine. Our Machine to Machine (M2M) service offering includes developing system capable of remote monitoring and controlling of machines, PLC’s, etc.

Measuring flow of fluids is an important requirement in process control in many industries. Requirements of precision and accuracy vary depending on the application i.e. water management vs. bottle filling. There are many technologies available to measure the flow including differential ultrasound, Coriolis, differential pressure and electromagnetic flow meters.

Of them, electromagnetic flow meter also called as “magmeter” is one of the most commonly used flow measurement systems. Due to its non invasive sensing, it is very much useful in especially measuring difficult corrosive fluids. Magmeters provide measurements irrespective of the fluid temperature, pressure, density and direction. Though they have limitation on non conductive and non magnetic fluids, they are widely used in water, waste, paper, chemicals, mining and food industries.

In this blog, we will discuss about the magmeter basics along with the flow measurement and instrumentation of the same..

Magnetic Flow meters – Basics

The key principle behind electromagnetic flow meter is Faraday’s law of electromagnetic induction. This law states that a voltage will be induced in a conductor moving through a magnetic field. The magnitude of the induced voltage is directly proportional to the velocity of the conductor, conductor’s length and magnetic field strength.

Mathematically we can express Faraday’s law as

E = kBLV


“k” is the proportional constant that can be calibrated for the device

“B” is the magnetic field strength

“L” is the spacing between the electrodes (flow tube diameter)

“V” is the velocity of the conductive fluid

“E” is the voltage measured across the electrodes.

Using the above principle, the Magmeters generate current that passes through the field coils generating a magnetic field. Fluid passing through the field generates an e.m.f proportional to the velocity that is captured using electrodes and measured. The overall system architecture is described in the following section.

Magmater architecture

Electromagnetic flow meters are primarily embedded systems which are divided into seven functional units as explained below.

The following diagram depicts the architecture of the electromagnetic flow meter.

Magmeter System Block Diagram

Magmeter System Block Diagram

Flow tube houses the field coil and the electrodes which are in direct electrical contact with the moving conductive fluid. The electrode picks up the voltage present in the fluid. The electrode element is an important consideration. There are many options available for electrode elements with different temperature drift, corrosion rate and electrode potential characteristics including Platinum, SS etc. Selection of the same depends on the type of fluid being measured along with the required durability.

Coil excitation unit generates electric current which excites the field coils according to the control signal from the processing unit in order to generate the controlled magnetic field. Different type of excitation signals and their construction are described in next section.

Signal conditioning unit translates the flow tube electrode output into a significant measureable signal that is to be used for flow measurements. Instrumentation for the same is explained in the later sections.

Processing unit is the heart of electromagnetic flow meter. The control signal for the coil excitation unit is provided by the processing unit. It also works on the signal obtained from the conditioning system with various statistical and mathematical formula and provides the final flow reading to the IO and user interfaces.

IO interface supports providing the flow information to the existing external device. There are many output formats available to communicate with the external devices such as pulse output, current or voltage output, relay output, RS485/RS232 serial communication etc. In addition to the output interface, flow meter may also support interfacing the external transmitters, sensors or transducers as a value added option. With these external sensor or transmitter interface, the flow meter can also provide additional information such as temperature, pressure etc.

User interface such as LCD display, keypads, LEDs etc provides manual operation such as setting, editing the flow meter configurations at the field.

Power Supply Unit provides a stable power supply as it determines the quality of the measurements made. The magmeter might be powered from an AC source or from a battery. Smart power management and component selection is necessary for long battery life for battery magmeters.

Flow Instrumentation

In this section, we will discuss about electromagnetic flow measurement and instrumentation for the same. Other units of the flow meter like IO, User Interface and Power supply are not in the scope of this blog.

Coil Excitation

There are different techniques available for exciting the field coil each with varying degrees of complexity and error correction as follows

DC current excitation: Oldest excitation technique used to generate the magnetic field by driving the field coil using a constant DC current. In this type of technique, due to inherent error build up, the quality of measurement is limited.

AC sine wave: In this technique, the field coils are driven with AC excitation. This technique has disadvantages such as electromagnetic disturbance and zero point drift.

Low frequency DC rectangle: Most commonly used technique in which the field coils are excited using constant amplitude, alternating direction current to achieve the low zero point drift.

Tri-state low frequency DC: This type of excitation is similar to the low frequency dc rectangle excitation, but the duty cycle is reduced to about half of that of the rectangle. With this method, the zero point calibration is done during the absence of the excitation current. This type of excitation consumes lesser power too.

Dual Frequency: In this type, usually 1/8 of power line frequency is modulated with higher frequency to minimize the noise effectively. This method provides fast response but its operation is complex compared to that of the previous excitation types.

As mentioned earlier, there are many ways to achieve the each above excitation techniques. Of them, low frequency DC rectangle excitation using MOSFET H-bridge with constant current sink circuit is most commonly used.

Transistor or MOSFET H-bridge can be used to switch the direction of the constant current flow. With MOSFET H-bridge circuit, the field coils will be excited in the positive and negative phase simultaneously. The control signal for the H-bridge is provided by the processing unit. The excitation frequency will be 1/16, 1/10, 1/8, 1/4, or 1/2 of the power line frequency.

The following figure shows the waveform of low frequency DC excitation.

Low Frequency Excitation

Low Frequency Excitation

The excitation current to the field coil should be constant and the level may vary according to the diameter of the flow pipes. A current level from around 150mA for smaller diameters to upward of 1A for larger diameters may be required.

Since the current should be constant, a reliable and accurate current sink circuit is needed. The traditional method of constant current sink is using a linear regulated current sink circuit. This circuit requires a fixed voltage reference, operational amplifier, transistor and the current setting resistor. This circuit together with the H-bridge provides good performance with low noise. But the disadvantage of this circuit is the power loss due to the linear drop of the large current across the large voltage. Hence heat sink is required which adds extra costs and PCB area.

The following figure depicts an example circuit model of the coil excitation unit using linear regulated current sink circuit.

Magmeter Coil Excitation Circuit

Magmeter Coil Excitation Circuit

The best alternative of this circuit is the constant current sink with switch mode power supply. This technique eliminates the losses and improves the system performance.

With some modifications, the above circuit can be extended to use with tri-state and dual frequency excitation.

Signal Conditioning

Signal conditioning circuit requires the most careful design of the instrumentation as it determines the accuracy of the measurement. The e.m.f induced in the fluid is received by the sensor electrodes in the flow tube and carried over shielded copper cables to anywhere from few centimeters to few meters. The signal has following features:

  • Based on the flow velocity, the signal induced can vary from few uV to few mV there by with a dynamic range more than 1000.
  • Due to the effects like electrochemical reactions and others, there is a large amount of noise introduced in the flow tube.
  • With a large cable length between the tube and electronics, more noise is introduced from other sources like power cables, adjacent meters and systems etc. In certain environments, even when a person walks over the cable, noises are induced.

Information related to the flow is available from the difference of the voltage between electrodes. To handle such a sensor signal, irrespective of the electrode material, the signal conditioning circuit must perform the following tasks,

  • Rejecting the common mode voltages
  • Amplifying the low level electrode signal
  • Filtering the DC component and further amplification
  • Level shifting to identify the forward flow or reverse flow

Typically the overall gain of the circuit is around 450 to 600. Most signal conditioning circuits found in flow meters performs these tasks in two or three stages. The following sub sections illustrate the three stage approach of electrode signal conditioning.

Input Stage

In the input stage, the common mode voltage is rejected and the electrode signal is amplified with a small gain. The input stage process must be accomplished with the precision instrumentation amplifier with the following characteristics,

  • Matched layout and laser trimmed resistors for low gain error, gain drift and high common mode rejection.
  • High input impedance to minimize the loss due to unmatched impedance between electrode and amplifier.
  • Low bias current and low offset current to minimize the current noise and common mode voltage.

Filtering and amplification stage

In this stage, the DC component and the higher frequency noise are removed by an active band pass filter or a cascade of amplifiers. Further the filtered signal is amplified so that the signal value is expanded to occupy the full voltage range of the ADC being used. Careful design of this stage is necessary to prevent unwanted signals from bands not of interest as well as noises inherent to this stage.

Level Shifting

The output from previous stages provides information about the flow. The amplitude of the signal reflects the fluid velocity. If the output is in phase with the coil excitation, it indicates on direction of flow and out of phase marks flow in opposite direction.

The signal is a bipolar that can be converted to unipolar using a small voltage usually fixed a half of the ADC reference value.

One of the simplest ways to achieve this is to use a simple adder circuit fed with the fixed reference voltage and the bipolar signal. The output can be directly fed to the ADC. For example, for an ADC with full scale input range of 2.5V, the fixed reference voltage could be 1.25V. If the ADC Value is above 1.25V, then the flow is in one direction and if below 1.25V, then the flow is in the opposite direction.

Design Considerations

Some of the aspects to be taken care during the design and development of the magmeter includes

  • The reference terminal of the unity gain differential amplifier must be driven using low impedance source. Driving from the high impedance source will result in poor CMR. The simple way to use the low impedance source is to drive using an Op-Amp buffer.
  • Choosing the high precision resistors in gain setting stages such as input stage, filtering and amplification stage.
  • Do not leave unused Op Amp sections in the circuit open.
  • Oscillations and noise might also be introduced from the AC power supply lines. Proper grounding of the flow tube and the electronics will help minimize the same.
  • Based on the fluid and sensor type, there might be different DC build up in each of the sensors. Care must be taken to reject this and process only the signal component of interest.
  • High precision and accurate ADC must be used for better reliability and accuracy.

Flow Measurement

Processing unit needs to incorporate intelligent algorithm for improved signal processing. After the flow velocity is found, the actual flow can be easily calculated based the flow tube diameter. Design of other units like IO, User Interface etc are quiet straight forward as they are primarily digital circuits as opposed to analog circuitry in Coil/Sensor conditioning.

This blog should provide a quick overview for the design and development of electromagnetic flow meters to begin with. With careful design of the instrumentation circuit, it is possible to achieve high level of precision in the magmeter. More features like variable gain, different types of excitations can be explored to improve the performance further.

Embien Technologies with proven experience in designing various instrumentation devices like flow meters, data acquisition systems, protocol converters etc is helping industries with its design services. Contact us to take advantage of our expert team of analog instrumentation engineers to design your instrumentation product.