American Magnetics 150A Portable Liquid Helium Level Meter (CE-Marked) - Manual (Page 6)

6 March 6, 2001
B. ACTIVE LENGTH CALIBRATION
1. Jumper the I+ and V+ contacts (pins 1 and 8)on the SENSOR connector together
and connect to one side of the calibration resistor. Jumper the I- and V- contacts
(pins 6 and 7) on the sensor connector together and connect to the other side of
the calibration resistor. The value of the calibration resistor should be (4.56
ohms) x (the active length of the sensor in cm); remember that the active length
of AMI standard sensors is 1 inch less than the overall length.
2. Temporarily install a short circuit (using a clip lead or other means) across the
calibration resistor.
3. Depress the READ switch.
4. Adjust the SPAN potentiometer located on the circuit board through the side
access hole in the lid until the display LCD reads 100.0. Refer to Figure 1.
5. Release the READ switch.
6. Remove the short from the calibration resistor.
7. Depress the READ switch.
8. Adjust the ZERO potentiometer located on the circuit board through the side
access hole in the lid until the display LCD reads 0.0. Refer to Figure 1.
9. Release the READ switch.
10. Repeat steps 2 through 9 until neither potentiometer needs adjusting.
11. Remove the jumper wires and calibration resistor.
12. The calibration procedure is complete.
13. Reconnect the sensor to the instrument.
IV. TROUBLESHOOTING
A. No LED power indication when the READ switch is depressed
1. Verify the sensor is properly connected to the SENSOR connector. The
POWER LED indicates proper sensor current; consequently, the POWER LED
will not light if the sensor is not connected properly even though batteries are
fully charged.
2. Recharge the batteries.
3. Check the condition of the internal batteries. Verify no corrosion exists.