How to Use FNIRSI SG-004A for Sensor Calibration

By Kunkune | Published: 2026-10-26

Category: How-to Guides

Learn step-by-step how to calibrate PT100 RTD sensors and 4-20mA transmitters using the FNIRSI SG-004A signal generator, with practical tips to avoid common mistakes.

Quick answer

Use the FNIRSI SG-004A signal generator in PT100 or 4-20mA mode to simulate sensor output, then verify your measurement system responds correctly—no separate calibrator needed.

Why the SG-004A fits sensor calibration work

The FNIRSI SG-004A is a multifunctional signal generator that doubles as a PT100 process calibrator and a 4-20mA source. That means you can simulate resistance values for RTD sensors or current loops for transmitters without needing multiple test instruments.

One limitation: the SG-004A does not measure sensor output directly—it only generates signals. You will still need a multimeter or your control system to read the response. This is typical for calibrators in this price range.

Common pitfalls when calibrating sensors

Many users forget to set the correct output mode before connecting. For PT100 calibration, the SG-004A must be in resistance simulation mode, not voltage or current mode. For 4-20mA transmitters, ensure you are sourcing current, not sinking it.

Another frequent mistake: using test leads with excessive resistance or poor connections. This introduces offset errors that can make a good sensor look faulty.

Step-by-step calibration procedure

Step 1: Set the output mode: Turn on the SG-004A and press the MODE button until the display shows 'PT100' for RTD sensors or 'mA' for 4-20mA transmitters. Confirm the correct range (e.g., 0–100°C or 4–20 mA) is selected. Checkpoint: If the display shows voltage (V) instead, you are in the wrong mode—switch back before connecting.
Step 2: Connect to the sensor input: Use quality test leads to connect the SG-004A output terminals to the sensor input of your controller, PLC, or display. For PT100, use a 3-wire or 4-wire connection if supported; for 2-wire, simply connect both leads. Common mistake: Loose or corroded connections cause erratic readings. Tighten terminals and inspect leads before proceeding.
Step 3: Simulate a known value: Use the rotary encoder or arrow keys to set a specific output value. For PT100, choose a standard temperature like 0°C (100.0 Ω) or 100°C (138.5 Ω). For 4-20mA, set 4 mA (0% span) or 12 mA (50% span). Checkpoint: Always start with a mid-range value to verify the system responds linearly before testing extremes.
Step 4: Read and compare the system response: Observe the reading on your controller or multimeter. It should match the simulated value within the system's accuracy specification. If not, note the deviation—this indicates a calibration offset. Common mistake: Ignoring small offsets. A 0.5% error at mid-range can grow to 2% at full scale. Adjust your system's calibration factor if possible.
Step 5: Repeat at multiple points: Test at least three points across the sensor's range (e.g., 0%, 50%, 100% of span). Record each deviation. A consistent offset suggests a simple gain or zero adjustment; non-linear errors may indicate sensor damage. Checkpoint: If deviations exceed the sensor's datasheet tolerance, replace the sensor rather than forcing a calibration adjustment.

Product facts

FNIRSI SG-004A Multifunctional Signal Generator PT100 Process Calibrator 4-20mA: SG-004A Multifunctional Signal Generator PT100 Process Calibrator 4-20mA This single device replaces a dedicated PT100 simulator and a 4-20mA calibrator, saving bench space and cost for field or lab calibration work.
FNIRSI SG-004A Multifunctional Signal Generator PT100 Process Calibrator 4-20mA