Series A12
Unisens
2-Wire Transmitter
O & M Manual
- 23 -
Rev-L, 7/15
To zero the transmitter, allow zero air to flow to the sensor for 5 minutes. If the sensor is located
in air known to be gas free, follow the steps below to adjust the zero.
Step 1 With the LCD indicating normal mode of operation, activate the MODE control repeatedly until the
display shows "CAL". Then activate the ENTER control. The display will change to "SEL" and
the "Z" (for Zero) flag on the display will light.
Step 2 Activate ENTER again and the display will change to an indication of the current gas
concentration. The value should be close to zero. Observe the display to be sure it is not either
increasing or decreasing.
Step 3 When the display value is stable, activate ENTER again and any small sensor offset will be
stored in memory. The display will change to "SEL" and the "S" (for Span) flag will light. If you
wish to span the sensing module, activate ENTER and proceed to the next section of this manual.
If you only wish to set the zero, activate MODE until the display indicates "donE". Activate
ENTER to return to the normal operating mode.
SENSING MODULE SPAN ADJUSTMENT
Adjusting the sensing module span requires a source of reliable span gas. If possible, a span
gas with a gas concentration of at least 25% of the full scale sensing module span is recommended. For
example, if the full scale span is 20 PPM, span gas of at least 5 PPM should be used. Many span gases
are available in convenient disposable cylinders, while other gases require a permeation system to
generate a reliable standard. DO NOT ATTEMPT TO ADJUST THE SPAN OF A SENSING MODULE
WITHOUT A RELIABLE SPAN GAS.
To adjust the sensing module span, proceed as follows:
Step 1 Advance through the transmitter program using the MODE and ENTER controls until the display
indicates "SEL" and the "S" flag is lit. This display is indicating that you can now select the span
mode.
Step 2 Activate ENTER and the display will indicate gas concentration. The "S" flag will remain lit.
Step 3 Screw a calibration adapter onto the sensing module as shown in Figure 8. Connect your span
gas source to the inlet fitting on the cal. adapter.
Step 4 Turn on the flow of calibration gas and allow it to flow for 5 minutes. The LCD display should
increase in response to the sensor being exposed to the target gas. After 5 minutes, use either
the UP or DOWN controls to adjust the value on the display to the span gas value.
Step 5 Activate ENTER and the new span constant will be stored in the sensing module. The display will
now indicate "donE". Activate ENTER to return to normal operation.
