DT Command — OneWire Temperature Query
The DT command allows querying temperature values measured by OneWire digital sensors (DS18S20, DS1822, DS18B20).
What is it for?
🌡️ Thermal monitoring — Reads current temperature from connected sensor
❄️ Cold chain — Verifies refrigerated transport temperature
🔥 Over-temperature — Detects critical conditions in equipment
📊 Age — Indicates how long ago the last reading was taken
This page describes the one or two sensor format used by legacy devices (C3, C5, SP, UL). On IoT devices the firmware always responds with all eight sensors concatenated, even if none are connected. For Spider IoT, Smart IoT and Zero IoT the reference is DT IoT Command.
Syntax
| Operation | Command | Description |
|---|---|---|
| Query | QDT | Reads current temperature |
Response
RDTSign1Temp1Age1Sign2Temp2Age2| Field | Description |
|---|---|
sign | + (positive) or - (negative) |
temp | Temperature in hundredths °C (4 digits) |
age | Seconds since reading (2 hex) |
Examples
Negative temperature
>QDT<
>RDT-156001+0000FF;ID=1234;*3A<
// -15.60°C ❄️, age: 1 second| Field | Value | Meaning |
|---|---|---|
| Sign | - | Negative temperature |
| Temp | 1560 | -15.60°C |
| Age | 01 | 1 second since reading |
Positive temperature
>QDT<
>RDT+285005+0000FF;ID=1234;*2B<
// +28.50°C 🌡️, age: 5 secondsTemperature: +28.50°C (5 seconds old)
Freezing
>QDT<Response:
>RDT-058002+0000FF...Temperature: -5.80°C (ideal for refrigerated transport)
No sensor connected
>QDT<Response:
>RDT+0000FF+0000FF...Age FF (255 seconds) indicates sensor disconnected.
Temperature Format
The value is expressed in hundredths of degrees Celsius:
| Value | Temperature |
|---|---|
| -5500 | -55.00°C (minimum) |
| -1800 | -18.00°C (freezer) |
| -0050 | -0.50°C (near zero) |
| +0000 | 0.00°C (freezing point) |
| +2500 | 25.00°C (ambient) |
| +3750 | 37.50°C (body temperature) |
| +8500 | 85.00°C (maximum) |
Compatible Sensors
| Model | Resolution | Conversion Time | Precision |
|---|---|---|---|
| DS18S20 | 9 bits | 750 ms | 0.5°C |
| DS1822 | 9-12 bits | 93-750 ms | 2.0°C |
| DS18B20 | 9-12 bits | 93-750 ms | 0.5°C |
The DS18B20 is most recommended for its precision and versatility.
See DT IoT Command for more details.
Age Interpretation
Age indicates time since last valid reading:
| Age (hex) | Seconds | Status |
|---|---|---|
| 00-05 | 0-5 | Recent data |
| 06-1E | 6-30 | Slightly outdated |
| 1F-3C | 31-60 | Possible problem |
| FF | 255+ | Sensor disconnected |
Related Reports
Include temperature in custom report
>SUC10 $TEMP| QDT,5,4<Only includes temperature value (4 characters).
Automatic report on temperature change
>SRL18E;TRG=DT(00)ch>200;ACC={GBR00L}<Generates report if temperature changes >2°C.
Compatibility
| Dispositivo | Notas |
|---|---|
C3Legacy | 1 sensor / 1 Port OW0 |
C5 SmartLegacy | 2 sensors / 2 Ports OW0 and OW1 |
SpiderLegacy | 1 sensor / 1 Port OW0 |
UltraliteLegacy | 1 sensor / 1 Port OW0 |
See Also
- OW Command - OneWire ROM ID query
- AR Command - Temperature thresholds
- DT IoT Command - Multiple sensors
- CXOW Command - OneWire configuration