Each energy meter used for billing must have a test output. An optical indication is mandatory. Beside this the meter can also have electrical test outputs (e.g. potential free contacts).
Today we only take care about the optical outputs.
Electromechanical meters have rotating disks with a black or red mark. Electronic meters have a flashing pulse diode.
In modern meter test equipments the optical output is detected by a scanning head. Typically the scanning head can pick up pulses from electromechanical- and from electronic meters.
Avoid solar radiation and rapid changes in the environmental illumination. This can cause false pulses and will spoil the meter test.
Click on START and watch the animation.
Scanning of Electromechanical Meters
Electromechanical (Ferraris) meters have a aluminium disk viewable in a window. The rotation speed of this disk is related to the actual power. The scanning head emits lights (a) which is reflected once the disk-mark passes the centre of the meter window. A light sensitive detector (b) picks up the light and converts it into an electronic pulse.
To adjust the contrast the scanning head sensitivity can be changed with a potentiometer. Once the scanning head is adjusted, it flashes on the rear side (c) simultaneous.
Scanning of Electronic Meters
Electronics meters have one or more LEDs for test output.
To test this meters the scanning head lights (a) should be switched off.
The scanning head is adjusted once the feedback LED (c) is flashing correspondent to the test LED.
Once the scanning head is adjusted, it forwards the pulses to an error calculator. This is done by wire or wireless (CLOU development). How this works we’ll see in a separate post.
Rotating- or Flashing Speed
Each test output has a meter constant. This constant gives us the energy related to one revolution respective one pulse. A pulse is in our case the gap between two consecutive flashes of the test diode.
You can use the pulse calculator to figure out the rotating/flashing speed in relation to different parameters.
Thank you for reading.
How does a scanning head work?