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 .

How to Use the Calculator

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.

Key Concepts of this Calculation

• 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.

Step 1: Understand the 4-20 mA Standard

• 4 mA: Represents the LRV (0% of the measurement range).
• 20 mA: Represents the URV (100% of the measurement range).

Step 2: Gather Required Information

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).

Step 3: Calculate the Percentage of the Signal

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

Example Calculation:

For a mA output of 12 mA:

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

Step 4: Calculate the Span

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

Example Calculation:

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

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

Step 5: Calculate the Lower Range Value (LRV)

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

Example Calculation:

This indicates that the LRV is 0 units.

Step 6: Calculate the Upper Range Value (URV)

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

Example Calculation:

This indicates that the URV is 2000 units.

Example with Negative LRV

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

Step-by-Step Calculation:

1. Measured mA Output: 8 mA

2. Process Variable (PV): -500 units
3. Calculate Percentage of Signal:

4. Calculate Span:

5. Calculate LRV:

6. Calculate URV:

Results of this Calculation

• 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.

What this Calculator Does?

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.

Why Use this Calculator?

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.