Apogee Instruments Guardian SM-500 / SM-600
Greenhouse climate monitor for PAR or ePAR, air temperature, humidity, CO2, VPD, dew point and pressure.
The Apogee Instruments Guardian SM-500 and SM-600 are fan-aspirated multi-sensor monitors that measure PAR (SM-500) or ePAR (SM-600), air temperature, humidity, CO2, vapor pressure deficit, dew point and barometric pressure in greenhouses, grow rooms and vertical farms. This Modbus RTU template reads all measurements, fan speed and device status, and lets you write the fan, averaging, calibration and communication settings from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 58, read and write
- Brand
- Apogee Instruments
- Key readings
- PAR or ePAR · Air temperature · Relative humidity · CO2 concentration · Vapor pressure deficit · Dew point · Barometric pressure · Fan speed
- Available commands
- Start measurements at power-on · Fan duty cycle · Fan darkness threshold · PAR multiplier and sensor offsets · Running average time · Modbus address and serial settings
- Compatible models
- Guardian SM-500 · Guardian SM-600
- Last updated
Registers (58)
58 read, 31 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| PAR / ePAR | µmol/m²/s | Read | |||
| Air Temperature | °C | Read | |||
| Relative Humidity | %RH | Read | |||
| CO2 | ppm | Read | |||
| Barometric Pressure | kPa | Read | |||
| Vapor Pressure Deficit | kPa | Read | |||
| Dew Point | °C | Read | |||
| Fan Speed | rpm | Read | |||
| Device Status | Read | ||||
| PAR / ePAR (Integer) | µmol/m²/s | Read | |||
| Air Temperature (Integer) | °C | Read | |||
| Relative Humidity (Integer) | %RH | Read | |||
| CO2 (Integer) | ppm | Read | |||
| Barometric Pressure (Integer) | kPa | Read | |||
| Vapor Pressure Deficit (Integer) | kPa | Read | |||
| Dew Point (Integer) | °C | Read | |||
| Fan Speed (Integer) | rpm | Read | |||
| Device Status (Integer) | Read | ||||
| Start Measurements at Power-On | Read and write | ||||
| Start Measurements at Power-On (Integer) | Read and write | ||||
| Fan Duty Cycle | % | Read and write | |||
| Fan Duty Cycle (Integer) | % | Read and write | |||
| Fan Darkness Threshold | µmol/m²/s | Read and write | |||
| Fan Darkness Threshold (Integer) | Read and write | ||||
| Running Average Time | s | Read and write | |||
| Running Average Time (Integer) | s | Read and write | |||
| Bluetooth Control | Read and write | ||||
| Bluetooth Control (Integer) | Read and write | ||||
| LED Indication | Read and write | ||||
| LED Indication (Integer) | Read and write | ||||
| PAR Multiplier | Read and write | ||||
| PAR Multiplier (Integer) | Read and write | ||||
| PAR Multiplier Factory | Read | ||||
| PAR Multiplier Factory (Integer) | Read | ||||
| PAR Offset | µmol/m²/s | Read and write | |||
| PAR Offset (Integer) | µmol/m²/s | Read and write | |||
| Air Temperature Offset | °C | Read and write | |||
| Air Temperature Offset (Integer) | °C | Read and write | |||
| Humidity Offset | %RH | Read and write | |||
| Humidity Offset (Integer) | %RH | Read and write | |||
| CO2 Offset | Read and write | ||||
| CO2 Offset (Integer) | Read and write | ||||
| PAR Multiplier Factory (Alt 108) | Read | ||||
| PAR Multiplier (Alt 109) | Read and write | ||||
| Slave Address | Read and write | ||||
| Slave Address (Integer) | Read and write | ||||
| Baud Rate | Read and write | ||||
| Baud Rate (Integer) | Read and write | ||||
| Parity | Read and write | ||||
| Parity (Integer) | Read and write | ||||
| Stop Bits | Read and write | ||||
| Stop Bits (Integer) | Read and write | ||||
| Model Number | Read | ||||
| Model Number (Integer) | Read | ||||
| Serial Number | Read | ||||
| Serial Number (Integer) | Read | ||||
| Firmware Version | Read | ||||
| Firmware Version (Integer) | Read |
Loading registers…
Send your device list
If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Show PAR, air temperature, humidity, CO2 and VPD per greenhouse compartment or grow room on one dashboard.
- Get an email alert when CO2 falls below your dosing target or VPD rises above a limit you choose.
- Keep a year of light, temperature and humidity history to compare growing conditions between crops and seasons.
- Alert on a low fan speed, so a blocked or failed aspiration fan is noticed before it affects the air temperature.
- Stop the fan before fogging or spraying with a scheduled automation, and switch it back on afterwards.
- Download the measurements as CSV for your own crop registration or climate reports.
Installation
Connect the white wire (RS-485 positive) and the blue wire (RS-485 negative) to the RS485 port of the ModbusCloud Gateway and the black wire to ground. Terminate the bus with 120 Ohm at both ends.
Tie the green wire to ground to select RS-485 and power the Guardian with 5.5 to 32 V DC on the red wire. The USB cable only supplies power and carries no data.
The Guardian ships with address 1, 19200 baud, 8 data bits, even parity and 1 stop bit. Change them in the Apogee Connect app if the bus needs other settings.
In ModbusCloud, add a Modbus device with protocol RTU, address 1 and 19200 8E1, then import this template.
Write 1 once to Start Measurements at Power-On. Then check that PAR, air temperature, humidity and CO2 show plausible values in ModbusCloud.
Things to watch for
The Guardian does not answer. What should I check?
Check 19200 baud, even parity, 1 stop bit and address 1, or the settings you chose in the Apogee Connect app. The green wire must be tied to ground for RS-485; tied to 12 V the Guardian talks RS-232. Swap the white and blue wires if nothing answers. If the Guardian has its own power supply, run a ground wire between the Guardian and the Gateway.
Why are all values 0 after a power cut?
To save energy the Guardian only starts measuring after the first read of a measurement value, and that first read returns 0. This happens after every power cycle. Write 1 once to Start Measurements at Power-On and the Guardian measures as soon as it has power. CO2 and humidity can still take up to 30 seconds after power-up to become accurate.
Why is each measurement in the list twice?
The Guardian gives every value as a precise floating-point number and as an integer copy multiplied by 10 or 100. The template scales the copies back, so both show the same value. Use the floating-point values on your dashboards. The integer PAR copy cannot show more than 3276.7, which bright sunlight or strong grow lights can exceed.
Can I change settings from ModbusCloud?
Yes. Writing is off per gateway by default, so request it for the gateway in the portal first, and read a setting before you change it. A new baud rate, parity or number of stop bits only takes effect after a power cycle, a new address at once. Never write 0 to Slave Address: that sets address 1 and resets the factory calibration. Write 0 to PAR Multiplier to return to the factory value.
Why is the fan running again after a power cut?
Fan control and Bluetooth control set over Modbus do not survive a power cycle. If you stop the fan for fogging or spraying, write the fan duty cycle again after a restart, for example with an automation. A duty cycle of 0 stops the fan; when it runs, the minimum speed is 40 %.
More Apogee Instruments templates
Want to see how it works?
