MODEL 158A 909GF197B
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Section IV – OPERATION
4.1 CALIBRATION ADJUSTMENTS
All the adjustments for calibrating the Model 158A
Level-Tel are located on the printed circuit board
assembly and consist of the following (see Figure
8):
4.1.1 Zero Adjustment (0% Process Level
Point)
The zero adjustment can be obtained by the use
of the Fine and Coarse Zero adjustments. The
Fine Zero adjustment is a multi-turn
potentiometer (approximately 20 turns). The
Coarse Zero adjustment is a 12 position switch.
Clockwise rotation of the zero adjustments will
increase the output signal. When used in
combination, the zero adjustments are capable of
varying the 0% Process Level Point through an
approximate range between 0 and 1000 pF of
terminal capacitance.
4.1.2 Span Adjustment
The span adjustment can be obtained by the use
of the Fine and Coarse Span adjustments. The
Fine Span adjustment is a multi-turn
potentiometer (approximately 20 turns). The
Coarse Span adjustment is a 12 position switch.
Clockwise rotation of the span adjustments will
increase the output signal.
4.1.3 Null Adjustment
The Null adjustment is a multi-turn potentiometer
(approximately 20 turns) that prevents interaction
between the zero adjustment and the span
adjustment during calibration of the instrument.
This adjustment is factory set and should not
require readjustment. However, calibration of
the null adjustment (Ref. Para. 4.3.2) will be
required if a shift of the 0% Process Level Point
of the instrument is experienced following
calibration of the span.
4.2 OPERATIONAL MODE
(For Models 158A – ( ) ( ) – E (2, 3) only)
Unless otherwise specified, the operational mode
for the optional alarms No. 1 & No. 2 of Models
158A – ( ) ( ) – E (2, 3) when they leave the
factory are as specified in Figure 7 of this manual.
The operational mode of either of the alarms may
be changed by relocating the links on the Alarm
Relay Modules. See Figure 6 for location of the
modules. TB3 is Alarm Module No. 1 and TB4 is
Alarm Module No. 2. Refer to Figure 9 and the
following paragraphs for detailed instructions on
how to change the links to obtain the desired
mode. The supply voltage to the instrument
should be disconnected when making this
change.
4.2.1 Low Level Fail Safe
Applications for low level detection should utilize
the Low Level Fail Safe (LLFS) mode which is
defined as a decrease in input signal level to
cause the relay to become de-energized or
“alarmed”. This mode is accomplished by
jumpering “A” to “B” and “C” to “D”. (Ref. Figure
9.)
4.2.2 High Level Fail Safe
Applications for high level detection should utilize
the High Level Fail Safe (HLFS) mode which is
defined as an increase in input signal level to
cause the relay to become de-energized or
“alarmed”. This mode is accomplished by
jumpering “A” to “D” and “B” to “C”. (Ref. Figure
9.)
A C
JUMPER LINKS
(SEE NOTES 1 & 2)
B D
TB3 OR TB4
AS SHOWN IN
FIGURE 6
NOTES:
1. JUMPER “A” TO “B” AND “C” TO “D” FOR LLFS
MODE OF OPERATION.
2. JUMPER “A” TO “D” AND “B” TO “C” FOR HLFS
MODE OF OPERATION.
FIGURE 9
MODES OF OPERATION
