Apogee Instruments SQ-618
ePAR sensor that measures photon flux from 400 to 750 nm, far-red included, for crops under sunlight and LED lamps.
The Apogee Instruments SQ-618 is an ePAR sensor that measures photon flux from 400 to 750 nm, far-red included, above or within crops in greenhouses, growth chambers and outdoors. This Modbus RTU template reads ePAR, 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
- 36, read and write
- Brand
- Apogee Instruments
- Key readings
- ePAR photon flux density · Immersed ePAR · Detector signal · Device status · Firmware version · Serial number
- Available commands
- Modbus address · Baud rate · Parity · Stop bits
- Compatible models
- SQ-618 · SQ-618-SS
- Last updated
Registers (36)
36 read, 24 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Calibrated Output ePAR | µmol/m²/s | Read | |||
| Immersed Output ePAR | µmol/m²/s | Read | |||
| Solar Output ePAR | µmol/m²/s | Read | |||
| Detector Millivolts | mV | Read | |||
| Device Status | Read | ||||
| Firmware Version | Read | ||||
| Calibrated Output ePAR (Integer) | µmol/m²/s | Read | |||
| Immersed Output ePAR (Integer) | µmol/m²/s | Read | |||
| Solar Output ePAR (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 | ||||
| Solar Multiplier | 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 | ||||
| Solar Multiplier (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 ePAR per greenhouse section on one dashboard and compare light above and below the crop.
- Put the SQ-618 next to a PAR sensor on one dashboard to see how much far-red your LED fixtures add.
- Download the ePAR history as CSV to work out the daily light sum per day, far-red included.
- Use an automation on ePAR 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.
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 clear shield wire 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 and remove the blue cap.
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 ePAR shows a plausible value under the lamps or 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 on 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 white and blue if nothing comes back. With a separate power supply, connect its ground to the Gateway ground. A powered sensor draws about 37 mA; much more points to a wiring or supply fault.
Why does the SQ-618 read higher than my PAR sensor?
The SQ-618 also counts far-red photons up to about 750 nm, which a PAR sensor that stops at 700 nm ignores. Under LED fixtures with far-red the difference can be large. Both readings are right for their own range, so compare sections and set alarm thresholds with the same sensor type.
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 ePAR cannot go above 3276.7 µmol/m²/s, so it can clip under very strong light.
How do I put several sensors on one bus?
Every SQ-618 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, Solar Multiplier, 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.
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