A Practical Guide to Selecting and Installing Your ABB LM80.A Pressure Transmitter
Selecting the right instrument and installing it correctly are the first steps toward achieving reliable process measurement. This guide walks you through the critical steps of selecting the correct ABB LM80.A pressure transmitter for your application and provides best practices for its installation and commissioning to ensure long-term accuracy and reliability.
Part 1: How to Select the Right ABB LM80.A Variant
Before ordering, answer these key questions to ensure you get the right model.
Step 1: Define the Measurement Type
First, determine what kind of pressure you need to measure:
- Gauge Pressure (LM80.G): Measures pressure relative to atmospheric pressure. This is the most common type, used for tank level, pump discharge, etc.
- Absolute Pressure (LM80.A): Measures pressure relative to a perfect vacuum. Used in applications like vacuum distillation or barometric pressure reference.
- Differential Pressure (LM80.D): Measures the difference between two pressures. Used for filter monitoring, flow measurement (via orifice plates), and level in pressurized tanks.
Step 2: Determine the Pressure Range
Select a transmitter with a range that comfortably encompasses your normal operating pressure. A good rule of thumb is to have the normal operating point at around 60-70% of the selected range. This avoids over-ranging damage and optimizes measurement accuracy within the most used part of the scale.
Step 3: Consider the Process Media and Wetted Materials
The chemical composition of the medium you are measuring is critical. You must select wetted parts (sensing diaphragm, flange) made of a compatible material. For most standard applications, stainless steel 316L is sufficient. For highly corrosive media (acids, caustics), options like Hastelloy C-276 may be required. ABB's datasheets provide detailed compatibility charts.
Step 4: Specify Electrical and Process Connections
- Electrical Connection: Choose the required connection type (e.g., 1/2" NPT conduit, M20 x 1.5 cable gland).
- Process Connection: Common options include 1/2" NPT, G1/2", or flange-mounted connections. Ensure it matches your existing piping or impulse lines.
Step 5: Decide on Output and Communication
The standard is a 4-20 mA analog output with HART protocol. HART is highly recommended as it allows for easy configuration, remote diagnostics, and calibration using a hand-held device without interrupting the 4-20 mA signal.
Part 2: Best Practices for Installation and Commissioning
A proper installation is crucial for accurate measurement.
1. Location, Location, Location
- Mount the transmitter close to the measurement point to minimize the length of impulse lines (the small pipes connecting the process to the transmitter).
- Avoid locations with excessive vibration or large temperature swings.
- Ensure the transmitter is easily accessible for maintenance and calibration.
2. Mounting Orientation
For liquid service, mounting the transmitter so the electrical connection points downward can help prevent moisture from entering the housing. Always refer to the manufacturer's manual for specific orientation recommendations.
3. Impulse Line Piping
- For steam or hot media, use condensate loops to protect the sensor from high temperatures.
- Keep impulse lines as short as possible and slope them to prevent trapping gas (in liquid applications) or liquid (in gas applications).
- Isolate valves are essential to allow for maintenance without shutting down the entire process.
4. Electrical Wiring and Grounding
- Use shielded twisted-pair cables for the 4-20 mA signal to prevent electrical noise interference.
- Follow proper grounding practices as outlined in the ABB LM80.A manual. A good ground is essential for safety and signal integrity.
5. Pre-Startup Checks (Commissioning)
Before putting the transmitter into service:
- Leak Test: Perform a pressure leak test on all connections.
- Power Up: Apply power to the transmitter.
- Zero Check: Verify the zero reading. With both impulse lines equalized (for gauge pressure, vent the process connection to atmosphere), the output should be 4 mA (or 0% if using a digital readout).
- HART Communication: Use a HART communicator to verify the device tag, range, and other parameters are correctly set.
Conclusion
By carefully selecting the correct ABB LM80.A model for your specific needs and following these installation best practices, you can ensure that your pressure measurement system will deliver reliable and accurate data for years to come, forming a solid foundation for efficient process control.
