Figure 1-40B.—Zeroing a control transformer by the voltmeter method

1-51 Figure 1-40A.—Zeroing a control transformer by the voltmeter method. Figure 1-40B.—Zeroing a control transformer by the voltmeter method. 4. Deenergize the circuit, reconnect the S1, S2, and S3 leads back to their original positions, and then connect the circuit as shown in view B. 5. Reenergize the circuit. Start with a high scale on the meter and work down to the 0- to 5-volts scale to protect the meter movement. At the same time, turn the stator of the CT to obtain a zero or minimum reading on the meter. Clamp down the CT stator, ensuring the reading does not change. This is the fine electrical zero position of the CT. Zeroing Multispeed Synchro Systems. If multispeed synchro systems are used to accurately transmit data, the synchros within the systems must be zeroed together. This is necessary because these synchros require a common electrical zero to function properly in the system. First, establish the zero or reference position for the unit whose position the system transmits. Then, zero the most significant synchro in the system first, working down to the least significant. For example, zero the coarse synchro, then the medium synchro, and finally the fine synchro. When you zero those synchros, consider each synchro as an individual unit and zero it accordingly.