TB 9-4931-217-40
Ratio Arm Calibration
a. Performance Check
(1) Turn all TI resistance indicating dials to 0 (zero) and set range switch to 1
MILLIOHMS.
(2) Connect equipment as shown in figure 1, connection B.
NOTE
Allow at least 6 minutes for thermal stabilization before
proceeding to (3) below.
(3) Measure resistance and record value on ratio worksheet (table 3) as X1.
NOTE
Typical values are shown in table 3 for measured resistance
and computed ratio. Actual values will vary with each TI.
(4) Repeat technique of (3) above for remaining range switch positions listed in table 3.
NOTE
Two measurements are required for 6 KILOHMS range switch
position, using connection B of figure 1 and the other, using
connection C. These readings are shown on worksheet as X6a
and X6b, respectively.
(5) Using values recorded on ratio arm worksheet, compute ratio range switch
position 1 MILLOHMS to 6 KILOHMS, using example below.
Computed ratio,
disregarding power-of-ten notation, will be between 0.99995 and 1.00005.
Ratio = X1
X6b
EXAMPLE:
Assume values of X1 and X6b to be 1.000019 and 100,001.7, respectively, then
Ratio = 1.000019 = 1.000001 X 10-5
100,001.7
(6) Repeat technique of (5) above for remaining ratios listed in table 3.
b. Adjustments. No adjustments can be made.
10. Final Procedure
a. Deenergize and disconnect all equipment.
b. Annotate and affix DA label/form in accordance with TB 750-25.