Table 8-1 Coarse Zero Adjustment; Table 8-2 Binary Count Sequence For Coarse Zero Jumper Pattern - Honeywell 7866 Operation And Maintenance Manual

Triple range digital h2 and co2 analyzer/indicator and gas sampling panel

Hide thumbs

Table Of Contents

Table of Contents

Troubleshooting

Coarse Zero Adjustment (R11 and R16)

It may be necessary at some time to return the control-unit 20-turn fine ZERO (R16) to its center-of-travel

position. To do so requires a jumper-wire change in the sensing unit.

Step

Open the sensing unit and observe the jumper pattern used at the top of the round circuit card

(terminal board at bottom). Note that each pin provided for the six jumpers is identified with a 1

or a 0. Determine the binary number formed by the jumper positions used and record this

number. The letters identify the color of the corresponding jumper.

If the analyzer output current or voltage is above zero or other low-end value and the ZERO

adjuster is at its counterclockwise limit, determine that binary number which is one digit lower

than the number recorded and change the necessary jumper positions to form this number.

For example, if the jumpers are positioned to form binary number 111001, then the jumpers

must be repositioned to form the next lower number binary 111000. Change the sixth jumper

from 1 to 0.

If the analyzer reading is below the low-end range value and the ZERO is at its clockwise

limit, the zero must be shifted upscale. Position the jumpers to form the next higher number,

e.g., from binary 011010 to 011011. Move the right-end jumper from 0 to 1.

Refer Table 8-2 for the sequence used in binary counting. The card is screened with MSB

(Most Significant Bit) and LSB (Least Significant Bit).

The above jumper change should permit the return of fine ZERO adjuster R16 to its center-of-

travel position and allow completion of the analyzer zero adjustment. If it does not, simply

increase or decrease the binary number by one digit more. A change of one binary count is

equivalent to one-half travel of control unit ZERO (R16). If jumpers are changed inadvertently

before the binary number has been recorded (or if thermistor detectors have been replaced)

re-establish the correct jumper pattern. Measure the sensing-unit current output by connecting

a meter in series with terminal 12 at the sensing unit while zero-gas flows through the sensing

unit. Proceed through the steps in Table 8-3 in numerical sequence only until the current

output measures between 250 µA and 240 µA. Jumpers that have been placed in their final

positions, not been moved, are marked X. Start with binary 32 (100000).

Table 8-2 Binary Count Sequence for Coarse Zero Jumper Pattern

MSB

LSB

000000

000001

000010

000011

000100

000101

000110

000111

001000

001001

7866 Triple Range Digital H