MIL-DTL-25576E
APPENDIX A
hole where the meter was located. If the digital millivolt meter gives negative readings during calibration,
reverse the leads that lead to the digital millivolt meter
A.4.3 Digital meter. It may be possible to find a suitable digital millivolt meter that can be
installed within the TDR case in lieu of the original meter. However, most digital millivolt meters are
considerably deeper than the original TDR meter and there may not be sufficient room to accommodate
the new meter within the TDR case. It may be possible, however, to obtain digital meters which have a
detachable display that could be mounted on the front of the TDR with the remainder of the digital meter
located within the TDR case (if there is room) or attached to the side or back of the TDR (some users may
want to connect the AC power input to the digital meter through the TDR on-off switch).
A.5 Calibration. The calibration procedure for the digital millivolt meter is the same as that for the
original meter. The Low Cal and High Cal controls are used to adjust the meter readings to agree with
the calibration tube ratings as before. Note the greater sensitivity of the digital millivolt meter may cause
some jitter, but this should only be in the tenth of a millivolt (i.e. TDR unit) range.
A.6 OPERATION
A.6.1 Tube Deposit Rater (TDR). Mark 8A Tube Deposit Rating methods. See ASTM D 3241.
A.6.2 Delta Spun TDR. With the digital millivolt meter, negative TDR ratings are possible and the
sign (i.e. plus [+] or minus [-]) of the TDR rating must be recorded as well as the TDR value. The pretest
rating must be algebraically subtracted from the post test rating to obtain the Delta Spun TDR rating. The
Delta Spun TDR shall be determined along the length of the JFTOT tube from position 14 to position 56
at 2-mm increments. The largest value shall be reported.
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