Signal Output

Zeroing signal output

Figure 5-3

1 mV Output: Canceling Baseline Offset (the self- ZERO function)

O+ 1.000 mV

1.0 mV maximum output level

 

 

 

 

U

 

 

 

T

 

 

 

P

 

 

 

U

 

 

 

T

0.9 mV usable

1.0 mV usable

V

dynamic range

dynamic range

 

 

 

O

ZERO

ENTER

 

L

 

 

pressed

 

T

 

 

A+ 0.100 mV

 

 

 

G

 

 

 

E

Constant 0.1 mV

 

 

detector background

 

 

signal

 

+ 0.006 mV

 

 

 

HP 5890 SERIES II electrical zero

0 mV

Effect of ZERO on the +1 mV Analog Output

The example in Figure 5•2is in terms of the +1 V analog output. In Figure 5•3,identical treatment is made for the +1 mV output, except that the signal is shifted to an offset somewhat above electrical zero. This ensures a small positive offset (about 6% of full scale) in pen position at a connected chart recorder, and permits uninterrupted plotting, even if a small negative baseline drift occurs.

Once current ZERO setpoint value is displayed for the desired signal channel, pressing ENTER causes the value to be changed to the current signal value.

Self• ZERO should be done only at times of quiet chromatographic activity (i.e., not during a run). To do so during an active run may cause a baseline shift at the recording/integrating device.

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