254764-001 Rev B 21
Adjusting Scanner Gain and Offset
Scanner gain and offset adjustment via commands is available in SV units that have the “A” circled on the
label that indicates focus distance. The adjustment capability is useful for adapting the unit to various
material types and scanning angles during the setup procedure. Knowledge of PRINTRONIX ScanVision
software is required for best understanding of the following description.
When setting SV scanner gain and offset, use ScanVision Reflectance Profile Mode as the guide to viewing
signal levels. The object is to have at least 6 lines high of signal amplitude for the bar code(s) being
verified. The bar code signal vertical placement (offset) should be within the yellow lines to ensure the
signal is in the linear range. All other objects’ amplitudes and placements are not important. A picture of a
“good” signal level is shown below in Figure 5.
To adjust gain and offset settings, first use the ScanVision Transmit SV Commands Screen to send a ~HT
command to the SV unit. In the reply, look for the line that reads [DACs] = nnn nnn nnn nnn where nnn =
numeric values. Example: a unit may read: [DACs] = 201 146 255 255. This indicates the current settings.
1.
The 201 indicates the value of the gain setting. The higher the value, the higher the gain and therefore
the higher the amplitude of the scan profile for a symbol. Max value is about 225.
2.
The 146 value indicates the offset setting. The higher the value, the lower the symbol placement is
offset on the graph.
3.
The command ~Hd101nnn sets gain where nnn is the three digit value.
4.
The command ~Hd201nnn sets offset where nnn is the three digit value.
5.
Use these commands to set the desired signal amplitude ( ~Hd101nnn) and locate the signal vertical
placement between the yellow lines ( ~Hd201nnn.)
6.
A few iterations of commands will probably be needed, therefore it will be necessary to access the
Transmit SV Commands Screen and Reflectance Profile Mode alternately.
Note: A short cut to the
Reflectance Profile Mode is accessed by pressing F3.
7.
Like most other SV commands – new scanner settings are enabled immediately when received, but to
be stored to non-volatile memory so they are maintained on a power up condition, the ~Hx command
must be transmitted after the desired settings are achieved.
Figure 5 – Desired Signal Amplitude and Placement
1. Bar code signal
amplitude at least 6 lines
high. (A more preferred
7 lines high is shown in
this example).
2. Bar code signal
placement within the
yellow lines.
