MIL-DTL-38219D(USAF)
APPENDIX B
ALCOR MARK 8A TUBE DEPOSIT RATER MODIFICATIONS
B1. SCOPE
B1.1 This appendix gives instructions for the modification of the Alcor Mark 8A Tube Deposit Rater (TDR) so that
accurate measurements of the Delta Spun TDR ratings can be obtained. This appendix is a mandatory part of the
specification. The information contained herein is intended for compliance.
B2. APPLICABLE DOCUMENTS
ASTM D3241
Standard Test Method for Thermal Oxidation Stability of Aviation Turbine Fuels
(JFTOT Procedure) (DoD adopted)
B3. SUMMARY
B3.1 JFTOT heater tubes often have a pretest Spun TDR rating of zero or below when rated with the Mark 8A TDR
in accordance with ASTM D3241. This occurs because the surface finish of the heater tube test section is difficult to
control and new heater tubes have pretest ratings which range from about -5 TDR units to about +5 TDR units. To
compensate accurately for differences in the pretest ratings of the JFTOT heater tubes, the pretest rating is
subtracted from the post test rating to obtain the Delta Spun TDR rating. However, the production model of the
Mark 8A TDR cannot rate tubes below the 0 TDR level since the range of the meter is 0 to +50 TDR units.
Accurate positive and negative TDR values can be obtained when the original meter is replaced with a digital
millivolt meter that can read both positive and negative voltages. (NOTE: If the modification instructions given
below are followed, 1 millivolt (mv) will equal 1 TDR unit.) This appendix gives the instructions necessary to make
this change.
B4. APPARATUS
B4.1 Alcor Mark 8A Tube Deposit Rater in accordance with ASTM D3241. Alcor Inc., 10130 Jones Maltsberger
Road, PO Box 32516, San Antonio TX 78284.
B4.2 Digital millivolt meter with a minimum scale range of ±50 mv and a minimum accuracy of ±2 percent at 50
mv. The digital millivolt meter must have its own internal power supply that is compatible with available AC
power. A suitable meter is the Simpson Model 2850, PN 22984, with a range of ±199.9 mv and input power
requirements of 120/240 vac, 50 to 400 Hz.
B4.3 A 1000 ohm resistor, 1/4 watt (required for Option 2, below).
B4.4 Suitable electrical wiring, connectors, and other hardware to connect electrically the digital millivolt meter to
the Mark 8A TDR and, if desired, to attach physically the digital millivolt meter to the Mark 8A TDR.
B5. PROCEDURE
B5.1 Option 1. Leave the Existing Meter in Place. This option will enable the use of the TDR with either the
existing meter or with the digital millivolt meter, but not concurrently. The two meters will not give identical
readings; therefore, the TDR must be calibrated using the meter selected for use.
B5.1.1 Connect the digital millivolt meter in parallel with the existing meter. It may be necessary to drill holes in
the TDR case to bring out electrical leads from the existing meter terminals to the digital millivolt meter. The 1000-
ohm resistor is not used with this option. To avoid confusion, it is suggested that the face of the existing meter be
covered when the digital millivolt meter is used.
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