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Chapter 4 Maintenance & Repair Series 820 Instruction Manual
4-10 IM-82-C
Step 4. Adjusting Linearity
First gain access to the printed circuit board inside the enclosure:
1. For units with the digital display, carefully rotate the display un-
til it hits the top plate. Slide the display’s two side panels up and
remove. Move the display aside taking care not to damage the
connecting cable.
2. Remove the two Phillips head screws from the top of the trans-
ducer enclosure. Remove the two Phillips head screws from the
back of the transducer enclosure. Pull the enclosure panels off.
3. Orient the transducer with the component side of the circuit
board facing you. Plug in the transducer and allow to warm up
for at least 30 minutes.
Step 5. Zero Adjust
Connect a DVM to the transducer output pins. Adjust the zero po-
tentiometer for 0.0 volts (4 mA) at zero flow.
Step 6. Calibrate 25%
Use the calibration standard to set a flow rate of 25% of full scale.
Adjust the span potentiometer for 1.25 volts (8 mA) at the output of
the transducer.
Step 7. Calibrate 50%
Increase the flow rate to 50% of full scale. If the output is within
+0.05 V (0.2 mA), no adjustment is necessary. If the output is be-
yond these limits, install a jumper block at J1 in the appropriate posi-
tion (see Figure 4-7). Adjust R25 for the proper reading.
Step 8. Calibrate 75% and 100%
Set the flow to 75% of full scale. If the output is outside the limits
set in Step 7, install a jumper block in J2 in the appropriate position.
Adjust R27 for the correct reading. Repeat this procedure for 100%
flow using R29. Repeat Steps 6 through 8 at least one more time.
Figure 4-7. Printed Circuit Board Component Locations