OK. Mine arrived over the weekend.
I haven't powered it up yet, but I can report that Hydreon RG-11 Optical Rain Gauge is far more than a substitute for a tipping bucket.
The unit runs on 9-30 VDC or 9-26 VAC, 15 MA nominal, 50 MA with the relay energized. 55 MA with internal heater on. It has a SPDT relay output, 24 VDC/AC 1 amp max. There is an internal 8 switch DIP to set the various modes. It's a well-made commercial quality unit.
It does, indeed, have a tipping bucket emulation mode (Mode 0). It will pulse the relay on every 0.01", or (settable) every 0.001" or 0.0001" (!) and has a similar metric mode down to 0.001mm.
The rain gauge correlation to a manual gauge or tipping bucket is not very close. From the web site:
Typically, most readings will be +/- about 30%, with some readings varying 2:1. This is not, however, a guaranteed limit.
and...
Not as accurate as a properly maintained Tipping Bucket, but a better choice for many applications.
We do not claim an accuracy specification for the RG-11. The RG-11 totalizes drops and drop size, and we have correlated that to tipping bucket data. A properly maintained tipping bucket, on the other hand, measures the water directly. Sometimes the RG-11 will read a bit high, sometimes a bit low. Over a long period of time we expect this to average out reasonably well, but this will depend on conditions.
It also has the following switch selectable modes:
Mode 1: It's raining. Just what it says, with various sensitivity settings, and a "dark detect" setting. An example of when you would use this is for automatic skylights (close when raining) or a retractable sunshade (retract when raining or dark).
Mode 2: Condensation Sensor. Senses condensation or frost on the surface. Adapts to the "clear" condition so that gradual buildup of dust is compensated for.
Mode 3: Wiper control. This is the genesis of the technology, building automatic windshield wiper controls for cars, trucks, boats.
Mode 4: Irrigation control. Wired to the Irrigation solenoids power, it stops irrigation during rain and up to 5 days afterward.
Mode 6: Drop detector. Pulses relay for every raindrop it detects, pulse width in multiples of 200 ms depending on drop size, or settable for multiple 100 ms pulses per drop depending on size.
All of the modes have various adjustments and enhancements that can be set to affect that mode's operation.
For the price, I could see having more than one of these installed, set to different modes.