After the fix, PT100 and PT1000 measurements can show the same temperature in engineering units, while the PT100 channel can cover 550 °C through an external transmitter. The AM2 RTD itself remains limited to -50 to 200 °C; changing gain cannot extend that measurement range.
Measurement objective and module boundary
The term same output here means the same displayed temperature when both sensors are exposed to the same actual temperature. It does not mean that a PT100 and PT1000 produce the same resistance. Their nominal resistances differ, so the input must use the correct sensor type when converting resistance to temperature.
The AM2 RTD converts supported RTD resistance directly into temperature over a fixed -50 to 200 °C550 °C therefore creates an incorrectly scaled indication.
| Requirement | Valid approach | Invalid approach |
|---|---|---|
| Measure PT100 or PT1000 within -50 to 200 °C | Connect and configure the correct RTD type on the AM2 RTD | Apply one common configuration without accounting for sensor type |
| Measure PT100 up to 550 °C | Use an external PT transmitter and a compatible analog input | Increase the AM2 RTD gain to stretch its fixed range |
Check 1: Read the configured channel range. Expect the AM2 RTD path to remain -50 to 200 °C, with no software setting that changes its physical input range to 550 °C.
PT100 and PT1000 channel configuration
Configure each direct RTD channel for the sensor actually connected. The input's sensor selection determines how measured resistance is interpreted. Selecting PT1000 for a PT100, or PT100 for a PT1000, prevents the two channels from agreeing even when their display scaling is identical.
- Identify the installed sensor from its documentation, terminal labeling, or a disconnected resistance measurement made under safe conditions.
- Assign the corresponding PT100 or PT1000 input type to its channel.
- Remove any gain or offset previously added to force the PT100 display toward 550 °C.
- Use the module's native temperature result directly for measurements inside -50 to 200 °C.
Wiring resistance, loose terminals, and mixed conductor arrangements can create channel-to-channel error. Compare the sensor wiring against the module connection diagram and use the required conductor configuration. Do not compensate for a wiring defect with a display offset; that hides an electrical error at one temperature and generally produces error elsewhere.
Check 2: Place both correctly configured sensors at one stable temperature inside the module range. Expect both displayed values to represent that temperature within the combined sensor, wiring, and input accuracy allowed by the project.
External high-temperature signal path
A PT100 requirement extending to 550 °C needs an external PT converter because the required temperature exceeds the AM2 RTD limit. Select a transmitter whose configured measurement span includes the complete operating range. A 0 to 600 °C transmitter range is one suitable example because it includes 550 °C.
The converter may provide 0-10 V, 0-20 mA, or 4-20 mA. Feed that output to an analog input compatible with the selected signal. The converter performs the PT100 resistance measurement and linearization; the controller then scales the analog signal into temperature. The AM2 RTD is not converted into a wider-range device by placing gain after its temperature value.
- Choose a PT100 converter with an input range covering the required maximum.
- Configure its temperature span and output mode.
- Connect the output to a voltage or current input rated for that signal type.
- Provide the transmitter supply and loop wiring specified by its documentation.
- Keep the existing PT1000 on the AM2 RTD if its process temperature remains within -50 to 200 °C.
Check 3: Inspect the complete signal path. Expect the PT100 to terminate at the external converter, the converter output to terminate at a compatible analog input, and every configured signal type to match the wiring.
Analog scaling for the PT100 transmitter
Scale the transmitter channel from its actual electrical endpoints to its configured temperature endpoints. Do not reuse the AM2 RTD gain setting. For the example assumption of a linear 0 to 600 °C transmitter, the engineering-unit calculations are:
For 0-10 V:
Temperature (°C) = Voltage (V) / 10 V × 600 °C
For 0-20 mA:
Temperature (°C) = Current (mA) / 20 mA × 600 °C
For 4-20 mA:
Temperature (°C) = (Current (mA) - 4 mA) / 16 mA × 600 °CAt 550 °C, those assumed mappings produce approximately 9.167 V, 18.333 mA, or 18.667 mA, respectively. If the selected converter uses different temperature endpoints, substitute those documented endpoints in the linear scaling calculation. Use the analog input's documented raw minimum and maximum if the program works from raw counts rather than volts or milliamperes.
Check 4: Apply a known midpoint signal. For the example 0 to 600 °C span, expect 5 V, 10 mA on a 0-20 mA output, or 12 mA on a 4-20 mA output to display 300 °C.
Channel agreement diagnostics
Compare PT100 and PT1000 channels only where their valid temperature ranges overlap. Above 200 °C, the AM2 RTD channel cannot serve as a valid comparison reference. Within the overlap, separate a fixed offset from a scaling error before changing the program.
| Observed symptom | Likely fault class | Diagnostic action |
|---|---|---|
| Large disagreement at every point | Wrong PT100/PT1000 selection or wiring fault | Verify sensor identity, channel type, and terminal connections |
| Agreement near one point but increasing error across the range | Incorrect gain, span, or transmitter endpoints | Test low, midpoint, and high points and recalculate the slope |
| Nearly constant difference across the range | Offset, lead resistance, sensor placement, or calibration difference | Remove software offsets and test both sensors at the same stable temperature |
| PT100 display reaches 550 °C only after increasing gain | Display rescaling beyond the module range | Restore native scaling and install the external transmitter path |
Two sensors mounted in different locations may report different real temperatures. Place them together in a stable test condition before treating disagreement as an input fault.
Check 5: Test at two or more stable temperatures inside -50 to 200 °C. Expect the two channels to track the reference trend without an error that grows because of incorrect scaling.
End-to-end commissioning verification
- Confirm that the direct AM2 RTD channels are configured for their actual PT100 or PT1000 sensor types.
- Confirm that the high-range PT100 uses the external converter rather than gain-adjusted AM2 RTD scaling.
- Inject or measure the converter's lower endpoint and expect the configured lower temperature.
- Test the electrical midpoint and expect the midpoint temperature; for a 0 to 600 °C span, expect 300 °C.
- Test a value near the required upper operating point. For the example span, expect the signal calculated for 550 °C.
- Compare PT100 and PT1000 indications at a stable temperature within their common valid range.
Check 6: Run the final process test from sensor through display. Expect correct agreement in the common range, a valid PT100 indication through 550 °C, and no dependence on an artificial AM2 RTD gain.
Frequently asked questions
Can I extend the AM2 RTD range to 550 °C with gain?
No. Gain changes the displayed scaling, while the AM2 RTD measurement range remains fixed at -50 to 200 °C. Use an external PT converter whose configured span includes 550 °C.
Does the AM2 RTD support both PT100 and PT1000?
The installation uses both sensor types, but each channel must be configured for the sensor connected to it. Compare their displayed temperatures only within the module's -50 to 200 °C
Can I use a 0 to 600 °C transmitter for a 550 °C maximum?
Yes. Scale its documented 0-10 V, 0-20 mA, or 4-20 mA endpoints to 0 to 600 °C, then apply a known signal near the required maximum and verify that the display reads 550 °C.