Center-Pivot Percent-Timer to Depth
The number the operator turns at the panel: the end-tower percent timer, converted to applied depth.
Example
You enter
- System flow Q (gpm) 800
- Irrigated area (acres) 125
- Revolution time at 100% timer (hr) 20
- End-tower timer setting (%) 50
You get
- Revolution time 40 hr
- Gross depth per pass 0.566 in
- Days per pass 1.67
Details, formula, and sources
revolution = revolution_100_hr x 100 / timer_pct; depth = flow x revolution / (452.6 x area). The depth is inversely proportional to the timer - dropping it from 100% to 50% does not halve the depth, it doubles it, which irrigators get backwards constantly. An 800-gpm pivot on 125 ac with a 20-hr full-speed pass lays 0.28 in at 100% but 0.57 in at 50%. Closes the loop on center-pivot runtime. An operating aid, not a scheduling design.
revolution_hr = revolution_100_hr x 100 / timer_pct; depth_in = system_flow_gpm x revolution_hr / (452.6 x area_acres); pass_days = revolution_hr / 24.
Center-pivot percent-timer to depth (USDA-NRCS center-pivot design; university extension), by name.
The percent-timer/depth relation is public irrigation-engineering material; the pivot design and panel calibration govern the actual application.
Estimate. AHJ and licensed professional govern.
Field names used by the API: system_flow_gpm, area_acres, revolution_100_hr, timer_pct, revolution_hr, depth_in, pass_days
- Inverse timer depth is proportional to 1 / timer% (100% is fastest and thinnest; 50% doubles the depth)USDA-NRCS / extension
- Full-speed pass revolution_100_hr is the machine's rated maximum-speed revolution time; the 452.6 factor is acre-inches to gallons over minutesirrigation engineering