DIYbanter - View Single Post - Wind Speed Problem with Heathkit ID-4001

In article , says...
In article ,
wrote:

I have a problem with my Heathkit ID-4001 Weather Station. The wind
speed works fine if there is any wind but when there is a calm wind
condition it occasionally starts giving erratic wind speeds. If it
should be reading zero speed, it reads zero and then jumps to a higher
wind speed, such as 32 and then back down to zero or up to 41. There
doesn't seem to be any pattern that I can discern. The actual wind
speed values tend to be random and when they occur appears to be random.
It can go for some time sitting at zero and then give an erroneous
reading or several erroneous readings in quick succession and then set
at zero for an another period of time. As soon the wind picks up it
appears to read the wind speed flawlessly.

Any ideas on what the problem might be or what to check for?

Does this system controller measure the speed by reading a voltage
from the sensor (with voltage being proportion to wind speed) or is it
counting pulses (1, or N pulses per revolution, hence frequency is
proportional to speed)?

If it's counting pulses, then I might suspect either of:

It is indeed counting pulses.

- A "bouncing" switch in the sensor, which is just barely making
contact at the point at which the sensor has stopped spinning, and
is vibrating open and closed. The cure for this would be a better
sensor-switch - one with enough hysteresis that it opens or closes
firmly and doesn't jitter back and forth.

It is not a mechanical switch. The pulse generator consists of an IR
LED that shines on IR sensor with a plastic disk in between that has a
series of black stripes painted around the edge of it. When the wind
cups spin, the disk spins so the black stripes interrupt the IR path
between transmitter and sensor generating pulses. The pulses then to go
to a base of a transistor that I assume is a switching transistor that
is either fully on or fully off. It is an NPN transistor in common
emitter configuration and the output of that is fed directly into the
CPU for counting the pulses in a given time frame for wind speed
determination.

- RF interference from a local transmitter, with the RF signal
"looking like" contact opens and closures to the control unit. The
cure here would be some amount of RF snubbing being added to the
line to the sensors - possibly wrapping the wires around some
ferrites, possibly adding a small amount of capacitance across the
line to shunt out the RF, or possibly both.

I thought about the possibility of noise pickup and put some a capacitor
across the line where it connects to the weather station and it did not
seem to help.

Thanks for taking the time to reply.