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Calibrating Raven Flow Meter: Sourcing Agricultural Crop Sprayer Valve Ratios
Quick Answer: A Raven flow meter calibration fails most often because the meter cal number is copied from the wrong tag or the valve ratio is left at a default value. For agricultural crop sprayers, the correct meter cal must come from the flow meter tag, the Raven console manual, or a verified test bench. Silver Automation Instruments supplies industrial flow meters that help ag service teams verify pulse per liter values and valve ratio response before the sprayer goes to the field.
Why the Meter Cal Number Is the First Gate
Raven rate controllers use a flow meter cal number to convert pulses into volume. A typical turbine flow meter on a crop sprayer may send 100 to 600 pulses per liter depending on pipe size and flow range. If the console is set to 140 pulses per liter and the actual meter sends 185 pulses per liter, the sprayer will under apply chemical by roughly 24 percent. This is why calibrating Raven flow meter values should start from the tag, not from another tractor.
Many operators skip this part. They enter a meter cal from a neighbor sprayer or from an old controller. We have seen this on customer sites in South Australia and West Java. The result is always the same. The boom section pressure looks normal, but the agronomist finds streaks in the field two weeks later.
Valve Ratio and Rate Hunting
The valve ratio, sometimes called valve cal or proportional gain on a Raven SCS 440 or SCS 460 console, controls how fast the regulating valve corrects flow. A valve ratio that is too high will overshoot the target. A valve ratio that is too low will make the controller slow to recover after speed changes. Both cause rate hunting.
In practice, sourcing agricultural crop sprayer valve ratios should follow the sprayer plumbing and the valve motor response. A 3 m boom trailer with a 20 L/min pump needs a different valve ratio than a self-propelled unit running 120 L/min through a 25 mm control valve. Do not copy a ratio from a different chassis.
How to Source the Correct Valve Ratio Without Trial and Error
Start with the Raven controller manual for the specific console model. For a Raven SCS 440, look under the control valve setup or the rate control calibration menu. Write down the flow meter pulse per liter value first. Then record the valve ratio setting for each boom section. For a new sprayer, the dealer should provide these values. For an older machine, check the valve motor tag and the flow meter tag before you change console settings.
If the original tag is gone, run a bucket test. Run clean water through the flow meter at a steady 10 L/min and count pulses over 60 seconds with a multimeter or a pulse counter. Convert the count to pulses per liter. This is a low cost way to recover a missing Raven meter cal number. Do not run the test with air in the line. Air bubbles create false pulses and the cal number will be too high.
Industrial Flow Meters for Verifying Raven Sprayer Calibration
We often recommend a reference meter on a test bench or on a trailer. For water based fertilizer and herbicide solutions, an electromagnetic flow meter from Silver Instruments works well. A DN15 or DN20 model with 316L electrodes and a PTFE liner handles most starter fertilizer blends and glyphosate mixes at 25 °C and 3 bar. The 4-20 mA HART output connects to a PLC or a paperless recorder so you can log flow rate against the Raven console reading.
For oil based adjuvants and thicker suspension
A Field Example From Central Queensland
Last year a spray contractor near Emerald in Central Queensland asked us for a reference meter to check a Raven flow meter on a 36 m boom sprayer. The console was set at 175 pulses per liter. Our DN20 electromagnetic flow meter measured the actual flow and logged it on a paperless recorder. The test showed the Raven meter was sending 190 pulses per liter. After the operator entered 190, the application rate matched the target within 1.5 percent. The valve ratio was then adjusted from 45 to 38 to remove a slow rate oscillation.
This kind of case repeats in Indonesia, Vietnam, Nigeria, and Saudi Arabia. A small calibration error of 10 pulses per liter can mean thousands of dollars in wasted chemical on a 2,000 ha season.
Recommended Silver Instruments Setup for Sprayer Test Rigs
For a mobile sprayer calibration trailer, we suggest a DN15 or DN20 electromagnetic flow meter with 4-20 mA HART, pulse output, and a local display. Add a pressure transmitter before the meter to confirm there is no cavitation. Keep the flow range between 2 L/min and 40 L/min for most crop sprayer pump tests. For flows above 60 L/min, use a DN25 electromagnetic flow meter.
If the sprayer uses a dry flowable or a suspension fertilizer, use a Coriolis mass flow meter. It is not cheap, but it removes the effect of viscosity and temperature on the reference measurement. Many agricultural chemical distributors in Thailand and Argentina use this setup to audit their field sprayers.
Contact Silver Instruments
Send us your chemical type, flow range in L/min, pressure in bar, temperature in °C, and pipe size DN. We will recommend a reference meter that matches your Raven calibration test bench or field sprayer audit kit.
Tel: +86-25-68650347. WhatsApp: +86-25-52155837. WeChat: +86 15365082610.
We sell to distributors and end users across Southeast Asia, Oceania, Latin America, Africa, and the Middle East. Ask for a quote today with your pipe size and flow range.
FAQ
1. What is a Raven flow meter cal number? It is the pulse per volume value that the Raven console uses to convert flow meter pulses into liters or gallons. Read it from the flow meter tag or the console calibration data.
2. Can I use a Silver Instruments electromagnetic flow meter on a crop sprayer? Yes, if the chemical solution is water based and has enough conductivity. For pure oil or very thick adjuvant, use an oval gear or Coriolis flow meter instead.
3. Why does my Raven rate hunt after calibration? The valve ratio or valve cal is usually too high. Lower the setting in small steps and watch the rate display for overshoot.
4. How do I find the valve ratio for an older Raven sprayer? Check the controller manual and the valve motor tag. If both are missing, contact a Raven dealer with the controller model and the valve motor part number.
5. Can Silver Instruments supply a reference flow meter for a sprayer test bench? Yes. Send us your flow range and chemical type. We will recommend a DN15, DN20, or DN25 electromagnetic flow meter or a suitable oval gear flow meter.