ALTA PAR Light Meter Configuration & Installation Guide
Overview
The ALTA® Wireless PAR (Photosynthetically Active Radiation) Light Meter monitors plants' ideal light wavelength for photosynthesis. It monitors light presence or absence, measures light intensity, and records daily saturation levels that affect plant health and growth.
Key Features
- The ALTA PAR Light Meter uses a blue-enhanced silicon photodiode with a spectral range of 389–692 nm +/- 5 nm to measure the specific wavelengths of light plants need for photosynthesis.
- The meter measures temperature-compensated Photosynthetic Photon Flux Density (PPFD) in µMol/m2/s.
- PPFD is the amount of PAR light (photons) that arrive at the plant's surface each second.
- The PPFD measurement is integrated throughout the day to produce the Daily Light Integral (DLI) in µmol/m2/day.
- It resets the DLI accumulation at a configurable time of day.
- The sensor reports immediately when configurable light level and DLI thresholds are breached to inform you of the most critical data as quickly as possible.
- The meter has a threaded M8 6-pin connector built into the lead for quick and easy disconnect or replacement as needed.
Settings to Configure
To edit the operational settings, choose the Sensor option in the left main navigation menu and then select the Settings Tab or icon to access the configuration page.
Sensor Name—The unique name you give the meter to identify it in a list and any notifications.
Heartbeat Interval—How often the meter communicates with the server if no activity is recorded.
Aware State Heartbeat—How often the meter communicates with the server while in the Aware State.
Low Light Threshold—The meter will report No Light if the light level falls below this threshold. There is no change to the Aware State or behavior. It's measured in micromoles per square meter per second (μmol/m²/s).
Saturated Light Threshold—The meter will report Saturated Light and observe aware behavior if the light level is above this threshold. The sensor will report immediately when transitioning between different light states. Measured in micromoles per square meter per second (μmol/m²/s). If the meter is aware for any other configured reason, the meter will report Aware. It will report immediately if the meter transitions across other configured thresholds or to a different light state.
Light Threshold Buffer—The meter will only transition from Aware to Not Aware when the light level is below the Saturated Light Threshold plus the buffer value. This feature prevents rapid transitioning between aware states when the sensor reads near a threshold.
DLI Reset Time—The meter will reset the photosynthetically active radiation daily light integral (PAR DLI) accumulation to zero each day. The meter will report a total 24-hour PAR accumulation at the reset time indicated. PAR DLI will reset to zero, and on the next Heartbeat, the meter will report the PAR DLI since the reset.
To correctly measure, track, and report PAR DLI based upon a full day, we recommend configuring the DLI Reset Time for 11 pm, 11:15 pm, 11:30 pm, or 11:45 pm. The configuration will not automatically adjust for daylight savings. That will require a manual adjustment if desired. When this configuration is sent to the meter, it will reset.
Measurement Interval—The frequency of photosynthetic photon flux density (PPFD) measurements used to calculate PAR DLI. When this configuration is sent to the meter, PAR DLI will be reset.
PAR DLI Threshold—The meter will report Aware, and when the PAR DLI value goes above this threshold—it will be measured in moles per square meter per day (μmol/m²/d).
Enable Temperature Compensation—When enabled, the meter will apply temperature compensation adjustments to the sensor transducer readings. If the meter base is not close to the same temperature environment as the element on the end of the lead, we recommend turning off temperature compensation.
Temperature compensation has a minimal effect at 20° Celsius. If the environment is kept at 20°C +/- 5°C, compensation will have less than a 1% impact on the sensor reading. If fast temperature swings occurring in less than 30 minutes are common in your application, we recommend that temperature compensation be turned off.
The temperature element is in the meter base, not the light-sensing element on the end of the lead. The temperature response will be prolonged since the temperature element is sealed in the meter base. It may not be well matched to the temperature the meter is experiencing during measurement. Keep this in mind when using temperature compensation. When this configuration is sent to the meter, the sensor will reset PAR DLI.
Finish configuration by selecting the Save button.
Select the Save button whenever you change any of the meter parameters. All changes to the meter settings will be downloaded to the meter on the following Heartbeat (check-in). Once a change has been made and saved, you cannot edit that meter's configuration again until it has downloaded the new setting.
Installation Steps
If this is your first time setting up your Monnit system, you must set up your iMonnit account and connect your ALTA Gateway to iMonnit before registering your sensor. See this article for steps to start: Creating an iMonnit account and refer to the ALTA Sensor General Information Guide.
Step 1.
Remove the sensor from the package and attach the antenna.
Step 2.
a. Register the meter in iMonnit.
b. Do not install the batteries until told to do so in iMonnit.
c. Refer to this walk-through guide and configure the sensor's Settings and Scale information in iMonnit for your specific application or use case.
d. Choose one of the following options for your use case: Very Low Light, Low Light, Moderate Light, High Light, Very High Light, or Full Light. To help you define the light level you plan to monitor, refer to the following light use case descriptions based on DLI metrics.
- Very Low Light = 4 mol / m2 / day
- Low Light = 7 mol / m2 / day
- Moderate Light = 13 mol / m2 / day
- High Light = 30 mol / m2 / day
- Very High Light = 52 mol / m2 / day
- Full Light = 65 mol / m2 / day
The above table can help you determine the DLI for your crops based on PPFD and time. The DLI is determined by the PPFD (at the top) and the number of hours that intensity is delivered. Understanding PPFD and DLI values is essential to successful monitoring using the PAR Light Meter. Refer to this table as you set thresholds for Actions and alerts in iMonnit.
e. Select Set to display the default settings for your product. Adjust your settings and pick the Save button when complete.
Step 3.
Determine the sensor's installation location. We recommend placing the sensor in the location and ensuring it reports to the gateway before final installation. See this article if you're using an ALTA Site Survey Tool to perform a site survey to determine the best sensor installation location.
Step 4.
a. After ensuring the sensor communicates with the gateway, mount the sensor. The sensor element must be level to measure PPFD incidents on a horizontal surface. Mount the element to the provided Mounting Bracket using the nylon screw provided.
Only use the nylon screw provided when mounting to insulate the non-anodized heads of the aluminum sensor head from the base to help prevent galvanic corrosion. For extended submersion applications, more insulation may be necessary.
b. To minimize azimuth error, mount the element with the cable pointing toward true north in the northern hemisphere or true south in the southern hemisphere. Azimuth error is typically less than 0.5 %, but it is easy to minimize by proper cable orientation.
c. In addition to orienting the cable to point toward the nearest pole, mount the element so that obstructions (e.g., weather station tripod/tower or other instrumentation) don't shade it. Once mounted, remove the blue cap from the element. The blue cap can be used as a protective covering when it's not in use.
d. The Mounting Bracket mounts the sensor element to a mast or pipe with an outer diameter of 1.3"–2.1". The Bracket has an integrated bubble level to make leveling accurate and straightforward for proper sensor installation.
Step 5.
a. Align and connect the cable using the arrows on the connector jacket and notch to ensure proper orientation.
If you disconnect the sensor for an extended period from an installation, protect the remaining half of the connector still on the station from water and dirt with electrical tape or another method.
b. Tighten the connectors firmly but finger-tight only. Don't tighten by twisting the black cable; only twist the metal connector. Don't use a wrench. An O-ring inside the connector can be overly compressed. Pay attention to thread alignment to avoid cross-threading. When fully tightened, one to two threads may still be visible.
Step 6.
Consider calibration for the Immersion Effect Correction Factor.
a. If needed, calibrate the meter for the immersion effect correction factor. When you submerge an ALTA PAR Light Meter in water, more incident radiation is backscattered out of the diffuser than when the sensor is in the air (1. Smith, 1969; Tyler and Smith, 1970). This phenomenon is caused by the difference in the refractive index for air (1.00) and water (1.33) and is called the immersion effect.
b. Without correction for the immersion effect, radiation sensors calibrated in the air can only provide relative values underwater (2. Smith, 1969; Tyler and Smith, 1970). Immersion effect correction factors can be derived by making measurements in air and at multiple water depths at a constant distance from a lamp in a controlled laboratory setting.
c. Apogee SQ-500 series quantum sensors have an immersion effect correction factor of 1.25 (serial numbers 2876 and above) or 1.32 (serial numbers 0-2875). This correction factor should be multiplied by underwater PPFD measurements to yield accurate PPFD.
d. You can find more information on underwater measurements and the immersion effect in this article: Apogee underwater PAR measurements.
1. Smith, R.C., 1969. An underwater spectral irradiance collector. Journal of Marine Research 27:341-351. 2. Tyler, J.E., and R.C. Smith, 1970. Measurements of Spectral Irradiance Underwater. Gordon and Breach, New York, New York. 103 pages
Step 6.
Review this Spectral Error article about how the ALTA PAR Light Meter was calibrated, how its PPFD measurements are calculated, and how to correct for the possible error.
Related Articles
What is the Daily Light Integral (DLI) in Crop Monitoring
What are PPFD and PPF Measurements
What is Photosynthetically Active Radiation
How to Correct a Spectral Error of the ALTA Par Light Meter
Understanding the Measurement Interval Sensor Configuration
Troubleshooting
Symptom |
Detailed Problem Description |
Solution |
| Not Checking into iMonnit | The meter lost the radio link to the gateway or never connected to the gateway. | 1. Power cycle the meter by turning the switch off for 60 seconds and then toggling it on. 2. Ensure the network is set up correctly in iMonnit (meter and gateway are on the same network). 3. Press the utility button on the gateway. If the network is set up correctly, reform the gateway. 4. Move the meter ~10 feet from the gateway. 5. Move progressively further from the gateway, ensuring at least two signal bars are showing. 6. Remember that the signal bars represent the signal from the previous message, not the current one. 7. We recommend taking two readings to verify signal strength. 8. Check the antenna on the gateway. |
| Low Signal | Radio signal strength in iMonnit is lower than expected. | 1. Ensure the gateway antenna is connected correctly. 2. Ensure the gateway antenna is optimally oriented to the position of the meter. |
| Comm Failure (Hardware Error) is Reported in iMonnit | The meter base cannot communicate with the measurement circuitry. Bit 1 of STS is set. | Contact Monnit for an RMA. Generally, this error can only be corrected through a repair by a skilled technician. |
| Temperature Out of Range error is reported in iMonnit | The temperature reads outside of the capable range. Bit 2 of STS is set. If the meter reads low, it reports -40.1° C; if over +125.1°C. | If temperature compensation is required, contact Monnit for an RMA; a skilled technician can only correct this error. |
| The meter doesn't seem to respond to light. Readings are either random or static, regardless of the light level. | Static or randomly fluctuating readings, regardless of light levels. | 1. Detach the lead via the connector and inspect for any corrosion, obstructions, or anything other than clean, straight interface pins. Good pins are an untarnished gold color. 2. If the connector looks good, reinsert the male and female ends completely, then tighten the collar. Power cycle the meter by switching it off and on, then verify it produces several good measurements. 3. If the problem persists, there may be a break somewhere in the cable. Contact Monnit for an RMA. |
| Sensor Imbalance is reported in iMonnit. | The meter is reading a light level outside of its capable range. Bit 3 of STS is set. | 1. Detach the lead via the connector and inspect for any corrosion, obstructions, or anything other than clean, straight interface pins. Good pins are an untarnished gold color. 2. If the connector looks good, reinsert the male and female ends completely, then tighten the collar. Power cycle meter and verify it produces several good measurements. 3. If the problem persists, there may be a break somewhere in the cable. Contact Monnit for an RMA. |
| Lower-than-expected readings | Lower-than-expected readings | Some obstructions can cause low readings. Below are a few to consider. 1. Moisture or debris on the diffuser 2. Dust during periods of low rainfall 3. Salt deposit accumulation from evaporation of sea spray or sprinkler irrigation water 4. Shade from any obstruction |