Apogee Instruments SQ-522
Full-spectrum quantum sensor that measures PPFD for crops in greenhouses, growth chambers and outdoors.
The Apogee Instruments SQ-522 is a full-spectrum quantum sensor that measures photosynthetic photon flux density (PPFD) above or within crops in greenhouses, growth chambers and outdoors. This Modbus RTU template reads PPFD, the detector signal, device status and identification, and lets you set the Modbus address and serial settings from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 34, read and write
- Brand
- Apogee Instruments
- Key readings
- PPFD · Immersed PPFD · Detector signal · Device status · Firmware version · Serial number
- Available commands
- Modbus address · Baud rate · Parity · Stop bits
- Compatible models
- SQ-522 · SQ-522-SS
- Last updated
Registers (34)
34 read, 22 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Calibrated Output PPFD | µmol/m²/s | Read | |||
| Immersed Output PPFD | µmol/m²/s | Read | |||
| Solar Output PPFD | µmol/m²/s | Read | |||
| Detector Millivolts | mV | Read | |||
| Device Status | Read | ||||
| Firmware Version | Read | ||||
| Calibrated Output PPFD (Integer) | µmol/m²/s | Read | |||
| Immersed Output PPFD (Integer) | µmol/m²/s | Read | |||
| Solar Output PPFD (Integer) | µmol/m²/s | Read | |||
| Detector Millivolts (Integer) | mV | Read | |||
| Device Status (Integer) | Read | ||||
| Firmware Version (Integer) | Read | ||||
| Slave Address | Read and write | ||||
| Baudrate | Read and write | ||||
| Parity | Read and write | ||||
| Stop Bits | Read and write | ||||
| Running Average | Read and write | ||||
| Heater Status | Read and write | ||||
| Model Number | Read and write | ||||
| Serial Number | Read and write | ||||
| Multiplier | Read and write | ||||
| Offset | Read and write | ||||
| Immersion Factor | Read and write | ||||
| Slave Address (Integer) | Read and write | ||||
| Baudrate (Integer) | Read and write | ||||
| Parity (Integer) | Read and write | ||||
| Stop Bits (Integer) | Read and write | ||||
| Running Average (Integer) | Read and write | ||||
| Heater Status (Integer) | Read and write | ||||
| Model Number (Integer) | Read and write | ||||
| Serial Number (Integer) | Read and write | ||||
| Multiplier (Integer) | Read and write | ||||
| Offset (Integer) | Read and write | ||||
| Immersion Factor (Integer) | Read and write |
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 PPFD per greenhouse section on one dashboard and compare light above and below the crop.
- Download the PPFD history as CSV to work out the daily light integral (DLI) per day.
- Use an automation on PPFD to send a webhook to your lighting control when light drops below a set level.
- Get an email alert when the sensor stops sending values, so a loose cable does not leave gaps in your light data.
- Let automatic monitoring flag a PPFD reading that stays frozen for hours while it normally changes.
Installation
Connect the green wire to ground to select RS-485. Wire white to RS-485 positive and blue to RS-485 negative on the ModbusCloud Gateway, and connect the shield to earth.
Power the sensor with 5.5 to 24 V DC: red to plus, black to ground. Mount it level with the cable pointing north in the northern hemisphere.
For more sensors on one bus, connect them one at a time and give each a unique address with Slave Address; every sensor ships with address 1.
In ModbusCloud, add a Modbus device with protocol RTU, address 1, 19200 baud, 8 data bits, even parity and 1 stop bit, and import this template.
Check that Calibrated Output PPFD shows a plausible value in daylight and drops close to zero when you cover the sensor.
Things to watch for
The sensor does not answer. What should I check?
Check that the green wire is connected to ground; on 12 V the sensor talks RS-232 instead of RS-485. Then check 19200 baud, even parity, 1 stop bit and address 1 in ModbusCloud, and swap the white and blue wires if nothing comes back. A powered sensor draws about 37 mA; much more points to a wiring or supply fault.
Why does every reading appear twice?
Each value is available as a precise floating point register and as an integer copy with a fixed decimal shift. Use the float registers for dashboards and alerts. The integer copy of PPFD cannot go above 3276.7 µmol/m²/s, so it can clip in full sun or under strong lamps.
Which PPFD value should I use in a greenhouse?
Use Calibrated Output PPFD for a sensor in air, above or within the crop. Immersed Output PPFD applies the correction for a sensor submerged in water, for example in a pond or aquarium.
How do I put several sensors on one bus?
Every SQ-522 ships with address 1. Connect one sensor at a time, write a new address from 1 to 247 to Slave Address, and change the address of that Modbus device in ModbusCloud. Never write 0: the sensor then returns to address 1 and also resets its factory calibration values.
Can I write calibration values or change the serial settings?
Writing is off per gateway by default; request it for the gateway in the portal. Multiplier, Offset, Immersion Factor, Model Number and Serial Number only accept writes after a procedure from Apogee Instruments, so leave them alone. Change Baudrate, Parity or Stop Bits only together with the same setting in ModbusCloud, otherwise the sensor stops answering.
Want to see how it works?
