Fluke 5720A service manual Auxiliary Amplifier Interface, 2-211. 5725A Interface

Theory of Operation 2

Analog Section Detailed Circuit Description

5220EN* is the output enable for octal latch U10. 5220ADIR* is the output enable for buffer U11. 5205EN* is the output enable for octal latch U9.

2-210. Auxiliary Amplifier Interface

A 5725A amplifier can be physically connected to the 5700A/5720A Series II. Only one can be used at a time. Depending on the amplifier’s mode of operation, the output of the Calibrator is either an ac or a dc voltage.

2-211. 5725A Interface

The Calibrator is designed to work in close connection with the 5725A Amplifier. The rear panel in this system provides relay switching for the 5725A signals. All voltage outputs from the 5725A are routed back to the binding posts on the Calibrator. All current outputs from the 5725A are sourced at the 5725A OUTPUT binding posts. You can configure the Calibrator to also source all its current outputs through the 5725A OUTPUT binding posts for convenience.

Connector J8 and Cable 4406 interface all the Calibrator I/O signals between the Motherboard and the rear panel. Connector J7 interfaces the Calibrator to the 5725A Amplifier. The interface between these two connectors is accomplished through relays K1, K2, and K6-K9. Relays K6-K9 break all the I/O lines except B-SENSE HI, B-OUT HI, V-GUARD, and B-IGRD, and connect them all to V-GUARD when the 5725A is not in use.

During 5725A operation, relays K1, K2, K6, and K7 switch the Calibrator analog signals B IN, B FB, B SNSLO, and PACOM to lines BOOST IN, B-FEEDBACK, B-SENSE LO, and BPA COM on connector J7.

High voltage output of the 5725A (B-OUT HI and B-SENSE HI) is connected to the Calibrator Motherboard via cable 4406 where it can be switched to the Calibrator binding posts by relays on the motherboard.

Relays K8 and K9 connect the 5725A current function lines I-RET, and B-CUR on connector J8 to B-IRTN, and B-CURRENT, on connector J7 when the 5725A is outputting Calibrator current (≤2.2A). Line B-RCL is used during 5725A calibration. Line B-RCL on J7 is connected to J8 through relay K6. Line B-RCL is routed via the motherboard to the Current assembly (A7) where it is switched to the calibrator RCL line by a relay.

2-212. Phase Lock In/Variable Phase out

The Oscillator Output assembly (A13) can be phase locked to an external signal connected to the PHASE LOCK IN BNC connector J6. Relay K10B connects the shell of this BNC connector to chassis ground through protection resistor R19 when the Calibrator is on internal operation, or to P LOCK LO when the Calibrator is phase locked to the external signal coming in on J6.

This incoming signal is called PHLK IN on the schematic. Relay K10A switches an external phase-lock signal from J6 to the input of Q1 and Q2. FETs Q1 and Q2 provide current limiting for PHLK IN. Signal P LOCK is routed to connector J8 where it is connected to the Oscillator Output assembly via the Motherboard.

Components CR1, CR2, VR1, VR2, R4, and R5 provide amplitude protection for the phase lock circuitry on the Oscillator Output assembly by limiting the amplitude of P LOCK.

The Variable Phase Out BNC connector (J5) is connected to P SHIFT and its shell is connected to PA COM by energizing relay K12. Signal P SHIFT is a fixed-amplitude variable phase signal generated by the Oscillator Output assembly (A13). Refer to the

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