Pulse Outputs in Water Meters Explained: What You Need to Know

In the flow meter and water meter industry, a pulse output is an electronic signal generated by the meter to indicate a specific amount of fluid has passed through it. Each pulse corresponds to a defined volume of water or fluid, such as one liter / 10, 100 and/or 1000 liters per pulse.

These outputs allow integration with data logging, Irrigation Controllers, RTUs, or monitoring systems, enabling accurate tracking and automation of flow measurement.

Pulse outputs are integral for automation, allowing meters to interface with Irrigation Controllers, SCADA systems, PLCs, or other monitoring setups. When choosing a meter with a pulse output, it's essential to consider the application’s flow rates, environmental conditions, and the compatibility of the pulse signal with receiving systems.

Types of Pulse Outputs & Where These Outputs Are Commonly Used

Reed Switch

• Found in mechanical flow meters and basic applications where simplicity is key.

Solid State

• Common in more advanced meters with programmable output needs, especially in revenue-based metering or where interference resistance is critical.

Optical

• Used in applications requiring very high-resolution data or in systems where precision flow tracking is essential.

Open Collector

• Typical of magnetic flow meters (Mag Meters) and other high-performance industrial devices. Often used in automation systems where versatility and reliability are needed.

Installation Example - Talgil RTU RF G5 ECO & Sensus WPD with Reed Switch

There are several types of pulse outputs based on the technology used:

1- Reed Switch Outputs (e.g. RD01):

A reed switch requires only two wires whereas most solid-state devices require three wires. A reed switch can be said to require zero power to operate it.

• A mechanical switch that opens and closes as a magnet moves past it.
• Common in basic meters and suitable for low-frequency applications.
• Simple and cost-effective but less durable under high-frequency operations.

Contact Type: Dry Contact

Power Requirements: No external power required

Pulse Value: Determined by the meter; non-programmable

Pulse Width: May vary based on flow rate; non-programmable

Directionality: Non-directional

Pros:

• Simple and effective
• Common in non-revenue metering
• Cost-effective and easy to use

Cons:

• Pulse width variability can complicate some applications
• Vulnerable to interference or tampering
• Limited to low-frequency applications

Reed Switch - Operation

2 - Solid-State Outputs (e.g., Sensus HRI, HRI-Mei):

A solid-state output is an electronic device that turns outputs on and off without moving parts.

• Use magnetic fields to generate pulses without physical contact.
• More durable and capable of handling higher frequencies compared to reed switches.
• Often used in industrial applications.

Contact Type: Wet Contact

Power Requirements: Self-powered (often battery-operated)

Pulse Value: Determined by the output device; factory programmable

Pulse Width: Factory programmable

Pros:

• Highly secure and resistant to interference
• Programmable for various applications
• Suitable for high-frequency metering

Cons:

• Higher cost compared to Reed Switch
• Limited lifespan depending on battery capacity

3- Optical Pulse Outputs:

An optical pulse output is a flashing LED or relay that indicates the power consumption of an electronic energy meter.

• Use light sensors and interrupters to generate pulses.
• Provide high accuracy and reliability but can be sensitive to environmental factors like dirt or moisture.

Contact Type: Typically a wet contact (requires clarification based on specific usage)

Power Requirements: Requires external power supply

Pulse Characteristics:

• High-resolution, high-frequency pulsing

Pros:

• Excellent for detailed, high-resolution flow tracking
• Accurate and fast response

Cons:

• Requires external power, increasing complexity
• Can be susceptible to environmental factors like dirt or moisture

4- Open-Collector Outputs (OC):

An open collector output is a type of pulse output that can be used with water meters. It's a solid state switching circuit that uses a bipolar junction transistor (BJT) to toggle the flow of current from the output signal wire to ground

• Require an external power source and a pull-up resistor.
• Versatile and compatible with a range of systems.
  

Contact Type: Wet Contact

Power Requirements: External power supply and pull-up resistor

Pulse Value: Determined by the external circuitry

Pulse Width: Adjustable with external configuration

Pros:

• Versatile and widely used in industrial systems
• Supports high-frequency pulses
• Reliable and secure

Cons:

• Requires additional configuration (pull-up resistor)
• Compatibility issues if power levels are mismatched

Example of a Water Meter Output Specifications

Pulse output voltage is a critical characteristic of flow and water meters, as it determines how the meter communicates with connected monitoring or control systems.

The type of pulse output can vary based on the meter's design and application requirements, and it generally falls into two main categories: volt-free (or dry contact) outputs and voltage-driven outputs (wet contact).

Volt-Free (Dry Contact) Outputs

How it Works:
Volt-free outputs generate pulses by physically opening or closing a circuit. This is typically achieved using components like mechanical switches or solid-state relays. No voltage is supplied directly by the meter; instead, the circuit relies on an external power source connected to the monitoring system. When the circuit is closed, it allows current to flow, signaling a pulse.

Advantages:

• Flexibility: Since no voltage is provided by the meter, the monitoring system can supply its own voltage, ensuring compatibility.
• Safety: The absence of voltage reduces the risk of electrical interference or damage to sensitive equipment.
• Simplicity: Easy to integrate with basic systems requiring only a simple "on/off" signal.

Voltage-Driven Outputs

• How it Works:
  Voltage-driven outputs produce pulses by varying the voltage level in the circuit. For example, a pulse might be represented by a change from 0V (low state) to a predefined higher voltage (e.g., 5V, 12V, or 24V). The voltage change acts as a signal that can be detected by connected monitoring devices.
  

Advantages:

• High Compatibility: Voltage levels can be tailored to standard digital inputs (e.g., TTL logic or industrial systems).
• Signal Strength: Voltage changes are robust, making them less prone to interference over long distances.
• Versatility: Ideal for complex monitoring systems requiring precise and high-frequency pulse detection.
  

Pulse Duration, Length & Pulse Transmitting

Pulse Duration: Refers to the time each pulse signal is active (high state). It is typically in the range of milliseconds, such as 50ms, 100ms, 500ms, but it can vary based on the meter and application.

Pulse Length: This measures the distance (or time) between successive pulses and depends on the flow rate and the meter's pulse resolution.

Faster flow rates product shorter pulse lengths, while slower rates lead to longer intervals.

Pro Tips

• Avoid Overpowering Reed Switches: Ensure the connected device doesn’t exceed the current rating of the reed switch to prevent damage.
• Check Compatibility: Verify that pulse output and receiving devices have compatible power requirements and configurations (e.g., avoid connecting two powered outputs).
• Prevent Interference: Use shielded cables and proper grounding to reduce noise and tampering risks.
• Match Output to Application: Select the appropriate pulse output type based on the required resolution, frequency, and environmental conditions.

Additional resources:

• Talgil Pulse Divider
• How to Convert 'Wet' contact into a 'Dry' contact - coming soon!