GE Corometrics 126, Service Manual

Page: 244 / 440

7-26 120 Series Maternal/Fetal Monitor Revision B
2015590-001
Calibration: Nautilus Tocotransducer Calibration
Calibration for Cat. No. (REF) 2264 AAX/BAX/CAX/DAX/EAX/FAX
1. Set the Gain (R15) and Offset (R5) potentiometers fully counterclockwise.
2. Set the Offset Trim (R6) potentiometer to its mid-position—approximately six
turns from fully counterclockwise.
3. Connect the positive lead of the digital voltmeter to TP6 on the FECG/UA
board; connect the negative lead to TP2 or TP3.
4. Turn on the monitor.
5. Plug the CMR Test Jack into the monitor’s
UA
connector.
6. Measure the voltage across the test points and record the value.
7. Replace the CMR Test Jack with the transducer to be calibrated.
8. Place the tocotransducer on a flat surface so that the button is face up, then
center the 52.5 gram weight on the pressure sensitive button.
9. Adjust the Offset (R5) and Offset Trim (R6) potentiometers so that the voltage
matches the reading recorded in 6
±
0.04 V. This voltage is referred to as the
“weight on” voltage.
‹ The Offset (R5) potentiometer provides course adjustment.
‹
The Offset Trim (R6) potentiometer provides fine adjustment.
10. Remove the weight and observe the voltage reading; this voltage is referred to
as the “weight off” voltage. A correctly adjusted transducer will show a voltage
change of +0.637 V
±
0.04 V. If the change is less, adjust the Gain (R15)
potentiometer counterclockwise to increase the gain. If the change is more,
adjust the Gain (R15) potentiometer clockwise to decrease the gain.
11. Repeat step 8 through step 10 until the change in voltage between the “weight
on” and “weight off” conditions falls into specification.
12. Torque seal all potentiometers.