Instrumentation Calculators

# Transmitter Calibration Span, LRV and URV Value Calculator from Measured 4 to 20 mA

Welcome to the Transmitter Calibration Span Value Calculator! This tool is designed to assist you in accurately determining the calibration range of your industrial transmitters using a 4-20 mA current loop .

1. Input the mA Output: Enter the current output from the transmitter (e.g., 12 mA).
2. Input the Process Variable (PV): Enter the value of the process variable corresponding to the mA output (e.g., 1000 units).
3. The LRV, URV, and Span values are obtained in calculated field of this calculator

This guide explains how to calculate the span, LRV, and URV of a transmitter in a 4-20 mA current loop.

• 4-20 mA Standard: A standard used in industry where:
• 4 mA corresponds to the LRV (0% of the measurement range)
• 20 mA corresponds to the URV (100% of the measurement range)
• Span: The difference between URV and LRV.
• 4 mA: Represents the LRV (0% of the measurement range).
• 20 mA: Represents the URV (100% of the measurement range).

You need two pieces of information:

1. Measured mA Output: The current output from the transmitter (e.g., 12 mA).
2. Process Variable (PV): The corresponding value of the process variable (e.g., 1000 units).

Use the following formula to calculate the percentage of the signal based on the 4-20 mA range:

For a mA output of 12 mA:

This means that 12 mA corresponds to 50% of the full measurement range.

The span is the full range of measurement for the transmitter. Use the following formula to calculate the span:

For a PV of 1000 units at 50% of the range:

This indicates that the full measurement range of the transmitter is 2000 units.

The LRV is the starting point of the measurement range. Use the following formula to calculate the LRV:

This indicates that the LRV is 0 units.

The URV is the endpoint of the measurement range. Use the following formula to calculate the URV:

This indicates that the URV is 2000 units.

Suppose a transmitter outputs 8 mA when the PV is -500 units.

1. Measured mA Output: 8 mA
1. Process Variable (PV): -500 units
2. Calculate Percentage of Signal:

4. Calculate Span:

5. Calculate LRV:

6. Calculate URV:

• LRV: -1000 units
• URV: 1000 units
• Span: 2000 units

These calculations show that with a given mA output and process variable, you can determine the calibration range of a transmitter, even for scenarios with a negative LRV.

This calculator helps you find three critical values for transmitter calibration:

1. Lower Range Value (LRV): The minimum value your transmitter can measure.
2. Upper Range Value (URV): The maximum value your transmitter can measure.
3. Span: The difference between the URV and LRV, representing the full measurement range.

Proper calibration of transmitters ensures precise measurement and control of process variables such as pressure, temperature, flow, and level. By inputting the measured milliampere (mA) output and the corresponding process variable (PV), this calculator provides you with the exact LRV, URV, and Span values needed for accurate calibration. This helps in:

• Ensuring Measurement Accuracy: Keeps measurements within expected ranges.
• Maintaining Process Precision: Facilitates correct scaling of measurements.
• Enhancing System Reliability: Enables consistent and dependable process control.

### Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe