Teledyne 7120 - NDIR analyzer - Manual (Page 76)

Infrared Analyzer Maintenance 5
5-9 Teledyne Analytical Instruments
(TPl) peak to peak voltage with
high impedance oscilloscope
if TP6 cannot be zeroed. If
greatly out of balance, check
for loose or dirty sample cell assembly.
(f) Try to execute a manual zero.
C. Meter reads Negative (a) ZERO control may be
misadjusted.
(with zero gas flowing Adjust control to bring indication
through analyzer) up to zero. (refer to Section 4).
(b) If zero indication unattainable with
ZERO control centered, monitor TP6
on preamp board. If greater than + or
Ä 3VDC, check waveforms at TPl
for balance.
(c) Check that infrared source is
operating. f cold check source
element resistance and connections.
D. Meter Up Scale or (a) Redo full calibarion.
Overscale
(b) Check for obstruction in sample
beam path.
(c) Check for excessive moisture in
plumbing and sample chamber. Clean
and replace sample chamber.
E. Insufficient Span (a) Recheck zero for excessive off-
Control (with span gas) set; monitor TP6 of preamp board
with zero gas and check for cell
contamination.
(b) Check modulation factor using
certified span gas. Full scale
concentration provides signal of
0-5 VDC at TPl of the Linearizer