I’m back with more information about my misfiring depth gauge.
As you might have found in my prior posts, I am using a SensComp Mini-AE sensor reporting to a BasiStamp PLC with A/D converter. This then radios results to a PC that allows me access via FTP to the results.
The problem has been: The SensComp Min-AE is producing a 10 volt signal regardless of distance to target. Adjusting the sensitivity doesn’t seem to alter that.
Facts relating to this:
The Mini-AE is mounted approximately 8 feet above the earth’s surface. On the ground directly under it is a white 4x4 foot sheet of plywood. The Mini-AE is mounted in a Davis weather instruments pagoda and mounted on a 3 foot arm from a pole. The area around it is fenced so that an area of snow more than 4 x4 feet directly below the sensor is undisturbed.
The Mini-AE has been leveled in all directions with a spirit level. The reflective surface on the ground has been leveled with a spirit level.
The snow is now 2 feet deep and has a hard crusty smooth surface. It is level as well. Approximate distance from the snow surface to the sensor is 6 feet.
No attempt was made to use the zero setting switches on the Mini-AE. It is a model #616105 which is powered by batteries and a solar charger producing 24 volts and the sensor produces a 0 - 10 VDC analog signal proportional to distance - 0 volts at 6 inches from the sensor (7.5 feet of snow), +10 VDC at 20 feet from the sensor. Of course with no snow on the ground, the sensor is about 8 feet from the ground, so the 10 volt depth signal voltage should never be seen.
Depth calculations are done by the Basic Stamp PLC based on the analog signal voltage and operator entered constants for sensor distance from bare gound.
The system was set up during the summer and worked perfectly on hard “targets.” The sensor would correctly read the distance to the plywood target base, and would read correctly the height of a stack of cardboard cartons used to simulate surfaces of varying heights.
Current state:
There is about two feet of very firm crusty snow with a smooth level surface under the sensor.
I just concluded some adjustment test in which I adjusted the sensitvity of the Min-AE as follows:
adjustment potentiometer position desired sensitivity my result
fully counterclockwise minimum 10 VDC
mid range mid range 10 VDC
fully clockwise maximum 10 VDC
These voltages were measured with a VOM at the connection to the Stamp PLC, so the bad readins are definitely the result of a high sensor reading, not a PLC software issue. When the sensor is powered off, the signal voltage is 0 VDC according to the VOM (normal expected result).
Discussion:
I don’t know what 10 VDC “means.” Obviously it means that the target is at or beyond 20 feet, but clearly that’s not the case here. Does it also mean the sensor is confused by false readings produced by a too sensitive setting? Could the sensor have gone bad? The bad signals began at the moment we received our first snowfall. The ground has not been bare since.
Hey - maybe I could test this simply by putting a “hard target” on top of the snow, like a piece of plywood! It should read correctly if the sneor is good, given it could do exactly that in September.
Thanks for any suggestions
Warpdrive