『Raven Flow Meter Calibration: Optimizing Crop Sprayer Liquid Valve Ratios』Related information(flow rotameter|digital flow meter|balo meter|hydraulic flow meter|volumetric meter|positive displacement meter|pitot tube flow meter|displacement meter|cfm meter|variable area flow meter|inline flow meter|differential pressure flow meter|calibrated flow meter|velocity meter|paddle wheel flow meter|oval gear flow meter|anemometer hvac|multiphase flow meter|doppler flow meter|thorpe tube flowmeter|heat flow meter)
Raven Flow Meter Calibration: Optimizing Crop Sprayer Liquid Valve Ratios
Quick Answer: Raven flow meter calibration matches the pulse output to the actual liquid volume. Adjust the liquid valve ratio so the sprayer controller holds the target rate without hunting. Silver Instruments supplies calibrated flow meters with 4-20 mA HART and pulse outputs to verify field performance.
Most crop sprayer issues show up as over application or under application. The Raven flow meter sends a pulse train to the console. The console uses the meter cal value to convert pulses into liters. If the pulse constant is wrong the whole calibration drifts. In practice we see this on many customer sites in Southeast Asia and Australia.
How the Raven Flow Meter Cal Works on a Sprayer
The Raven flow meter sits in the main spray line. It measures liquid flow and outputs pulses. A common value is 100 pulses per liter. Some older units use 50 pulses per liter. You need to enter the pulse per liter value into the Raven controller. If the value is off by 10 percent the application rate is off by 10 percent. That is simple math.
Liquid valve ratio is different. This parameter controls how fast the regulating valve corrects flow when the sprayer speeds up or slows down. A low valve ratio causes slow valve response. A high valve ratio causes the valve to overshoot and hunt. We have seen spray rigs in Vietnam swing 15 percent around the set rate because the valve ratio was too aggressive.
Step by Step Calibration Without Special Tools
First clean the flow meter strainer. Debris in the turbine or paddlewheel causes random pulse errors. Then run a catch test. Use a clean bucket or a calibrated vessel. Run the sprayer for one minute at the normal working RPM. Measure the actual volume caught. Compare it to the console readout.
If the console shows 10.0 liters and the bucket holds 9.3 liters the meter cal is high. Divide the console value by the bucket value. Multiply the current meter cal by that factor. For example a current meter cal of 100 pulses per liter would become 107.5 pulses per liter. Enter the new value and repeat the catch test.
Now set the valve ratio. Start at 2.5 for most Raven systems. Run a step test. Change the speed setting by 20 percent. Watch the flow readout. If the controller reaches the new target in 3 to 5 seconds and stays steady the ratio is fine. If it takes more than 8 seconds lower the ratio by 0.3. If it overshoots by more than 5 percent raise the ratio by 0.3. Each change needs a new test run.
When to Replace a Raven Flow Meter Instead of Calibrating
Some flow meters fail calibration because of bearing wear, cracked turbine blades, or chemical swelling. If the pulse output is not repeatable between identical catch tests the meter body or rotor is worn. Calibration will not solve that. Silver Instruments supplies electromagnetic flow meters and oval gear flow meters for crop sprayer retrofits. Our electromagnetic flow meter with DN15 or DN20 connection has no moving parts. It handles many liquid fertilizers and herbicides. It outputs a pulse signal and a 4-20 mA HART signal. That gives the Raven console a clean pulse input and gives a separate data logger an analog signal.
For low flow chemical injection systems an oval gear flow meter works well. We supply oval gear flow meters with 0.5 to 20 L/min ranges. The PT100 temperature compensation helps keep accuracy
Valve Ratio Values We See on Real Sprayers
For a 24 meter boom with a Raven 450 console the valve ratio often lands between 2.2 and 3.0. For smaller 12 meter booms we see 2.5 to 3.2. The right number depends on boom width, nozzle count, pressure, and pump response. Do not copy a valve ratio from another machine. Use the step test.
Here is the thing about pressure based sprayers. The flow meter and valve ratio work together. If the pressure sensor is drifting the console may fight the valve. Check the pressure transducer output with a known gauge. Silver Instruments supplies pressure transmitters with 0.5 percent accuracy for this check.
Silver Instruments Flow Meters for Sprayer Calibration
Our team can supply a reference flow meter for your workshop or mobile service trailer. A common setup is a Silver Instruments electromagnetic flow meter on a test bench. The Raven flow meter connects in series. You pump water through both meters for 60 seconds. Compare the totalizer values. This method gives a fast pass or fail result. Because the reference meter has fresh calibration data from our factory you can trust the reading.
We work with sprayer dealers and contractors in Indonesia, the Philippines, Australia, Mexico, Nigeria, and Saudi Arabia. Last year a customer in Vietnam asked us for a small electromagnetic flow meter to calibrate Raven units on 30 self-propelled sprayers. We supplied 20 units with DN20 flanges and pulse outputs. The customer cut calibration time from 45 minutes per machine to 20 minutes.
FAQ: Raven Flow Meter Calibration and Liquid Valve Ratio
What is the normal meter cal range for a Raven flow meter?
Most Raven turbine flow meters fall between 50 and 150 pulses per liter. The correct value depends on the flow meter model and nozzle plumbing. Always run a catch test to verify.
How often should I calibrate a crop sprayer flow meter?
We recommend a catch test at the start of each season and after changing nozzles or plumbing. In heavy use a monthly check is safer.
Why does the flow rate oscillate on the Raven console?
This usually points to a valve ratio that is too high or a worn flow meter rotor. Reduce the valve ratio by 0.2 to 0.4 and run the step test again.
Can I use a Silver Instruments electromagnetic flow meter with a Raven console?
Yes. Most Silver Instruments electromagnetic flow meters can be configured with a pulse output that matches the Raven input range. No moving parts means less drift in dirty spray fluids.
What is the best liquid valve ratio for a 24 meter boom?
There is no fixed best value. A 24 meter boom commonly lands between 2.2 and 3.0 with a Raven 450 console. Run a speed step test and adjust until the flow stabilizes in 3 to 5 seconds.
For a quote on a Silver Instruments flow meter send your liquid type, flow range in L/min, pipe size in DN, pressure in bar, and temperature in degrees Celsius. Contact Silver Instruments. Tel: +86-135-1213-1526, WhatsApp: 86-135-12131526, WeChat: +86 13512131526. More technical data is at flow-meter.com.au
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