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RetroSign GR1 & GR3 · Retroreflectometer
Note on error sources
Before measuring
The RetroSign is factory calibrated; nevertheless, begin important measurements sessions with a calibration, dust and
smear from touching the optical surfaces might influence the measured values considerably.
It is very important to keep the instrument front lens and the white reference cap clean.
See also
Section 4 - Maintenance
.
Instrument orientation
The RetroSign can take measurements without being in close contact with the sign surface. But to obtain the most relia-
ble results the front of the RetroSign should be in contact with, and perpendicular to, the sign surface when taking mea-
surements.
Sign conditions
The optical property of a sign alters when the retro reflective material becomes wet. The RetroSign can take measure-
ments on wet or dewy sign surfaces but readings are not comparable with readings taken on dry signs.
Because of the special optical properties of micro prismatic sheeting, precautions like turning the instrument correctly
and holding it vertical should be taken to get correct readings. Always use the RetroSign in the angle specified for the
sign.
Normally the RetroSign instrument must be held in the vertical position.
Leakage
During each measurement the RetroSign automatically evaluates the leakage (optical background signal) and the result
are compensated before read out. Leakage will under normal conditions not be significant. Nevertheless, leakage may
occur and a warning will be shown in the display. Leakage is primarily caused by stray light entering the optics between
the sign and the instrument.
Instrument leak, drift and offset errors are compensated for by means of data obtained during the calibration procedure,
so perform the calibration procedure carefully.
Low battery condition
The instrument always monitors the battery voltage and automatically blocks for further measurements when the battery
voltage gets very low. Due to the nature of the battery it may happen, when the instrument is turned on, that the voltage
will be high enough to start a measurement but not to turn the light source on causing the measurement to fail.
Doing measurements with a nearly discharged battery should be avoided as this might influence the measured values.
