Offset Tests

TM 9-2320-279-20-1

Instructions (Cent)

2-16. SIMPLIFIED TEST EQUIPMENT FOR INTERNAL COMBUSTION ENGINES

INTRODUCTION

The STE/ICE VTM is made to perform a test by setting the TEST SELECT switches to

the test number and pressing the TEST button. For some tests, an offset test is required before the test

itself can be performed. This is done by selecting the number of desired test and holding the TEST button

down until the VTM displays the prompting message CAL.

The offset test cancels characteristic differences in the VTM, test leads, and transducers. It zeros the

meter. Once the offset test is performed, the VTM automatically corrects for the offset before displaying

measured values. The displayed offset value should be checked against limits on the Vehicle Test Card. If

the displayed value is outside these limits, either the transducer or the test cable is faulty and must be

replaced. This is another form of self-test. Offset tests are done in both the DCA and TK modes of

operation. At the beginning of the DCA mode, all offset test numbers are dialed into the VTM. In the TK

mode, the offset is performed when each transducer is connected. All tests requiring offset are identified

by a star(*) on the flip cards and by OFFSET LIMITS on the Vehicle Test Cards. The offset test is performed

with the test probe cable or transducer connected to the VTM. Care should be taken that no stimulus is

being applied to the transducer. Test probe cable leads should be shorted together. To perform an offset

test, dial the test number into TEST SELECT. Press and hold TEST button until the prompting message

CAL appears on the display. In a few seconds after release of TEST button, a number will appear. This is

the measured offset value associated with the test probe cable or transducer or transducer and cable.

These tests are used to change (or control) the way a vehicle testis displayed, or

(4) Control

the way it is run. There are five (5) control tests.

01 Interleave (alternates RPM with next test measurement)

02 Display minimum value for next test

03 Display maximum value for next test

04 Display peak-to-peak value for next test

05 Initiate S1 full power simulation (Not applicable to M977 series vehicles).

Control tests 01, 02, 03, and 04 specify the action to be taken by the next test only. Any test dialed in after

the test that is being controlled will cancel the effect of the test.

This test alternately measures engine speed and a second parameter such as

Interleave

fuel pressure or alternator voltage. To start interleave, dial 01 into the Test SELECT switches and press the

TEST button. The prompting message PASS will signal the operator to dial in the second test number and

again press the TEST button.

(Test 02). This test displays the minimum value measured during a test. To start

Minimum

a minimum value display, dial 02 into the TEST SELECT switches and press the TEST button. The

prompting message PASS will signal the operator to dial in the desired test number and again press the

TEST button. The minimum value is displayed and updated whenever a lower minimum value is measured.

Entering 02 and the test number again will reset the process and a new minimum value will be displayed.

03). This test displays the maximum value measured during a test. To

Maximum

start a maximum value display, dial 03 into the TEST SELECT switches and press the TEST button. The

prompting message PASS will signal the operator to dial in the desired test number and again press the

TEST button. The maximum value is displayed and updated whenever a higher maximum value is

measured. Entering 03 and the test number again will reset the process and a new maximum value will be

displayed.

Peak-to-Peak Value (Test 04). This test displays the peak-to-peak value of

output

volts (82), 45-volts DC (89), 1500 amps DC (90), and battery volts (67). Electrical peak-to-peak is for

measuring dwell variation. To start a peak-to-peak measurement, dial 04 into the TEST SELECT switches

and press the TEST

The prompting message PASS will signal the operator to dial in one of the four

test numbers (82, 89, 90, 67) and again press the TEST button.

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