Fluke 5720A service manual Digital Section Detailed Circuit Description, Front/Rear Binding Posts

5700A/5720A Series II Calibrator

Service Manual

2-20. Front/Rear Binding Posts

An internal cable can be configured to enable either the front panel or panel binding posts. When compared to front panel binding posts, the rear panel provides the same OUTPUT HI, OUTPUT LO, SENSE HI, SENSE LO, AND V GUARD functions. Also, the rear panel provides an I GUARD (current guard) connection for use when the Calibrator is supplying low-level ac current through a long cable. Use of the I GUARD connection removes errors introduced by leakage through such cables. The rear panel binding posts do not provide an AUX CURRENT OUTPUT connection. The procedure to disable the front panel binding posts and enable the rear panel binding posts is to be done at Service Centers, although it is described in this manual in Section 4.

2-21. Rear Panel Assembly (A21)

The Rear Panel assembly provides physical and electrical connections for the auxiliary amplifiers, along with RS-232-C and IEEE-488 interface connections. Relays on the Rear Panel assembly are used as the interfaces for the 5725A amplifier, or for switching the PHASE LOCK IN and VARIABLE PHASE OUT signals.

A 5725A auxiliary amplifier can be physically connected to the Rear Panel assembly of the 5700A/5720A Series II at J7. Only one amplifier can be in use at one time.

∙The Rear Panel assembly provides relay switching for 5725A signals. Voltage outputs from the 5725A are routed to the binding posts on the Calibrator. Current outputs are soured at the 5725A OUTPUT binding posts. An alternate configuration is also available, allowing for routing of Calibrator current outputs to the 5725A OUTPUT binding posts.

2-22. Filter PA Supply Assembly (A18)

The Filter/PA Supply assembly incorporates two sections. The first section contains filters and regulators for some of the in-guard low-voltage supplies, and the second contains the power supply for the Power Amplifier output. Theory for each section is discussed separately.

2-23. Digital Section Detailed Circuit Description

Detailed descriptions of each assembly in the digital section are provided here.

Simplified schematics and block diagrams are provided to supplement the text.

2-24. Digital Power Supply Assembly (A19)

The Digital Power Supply assembly receives ac voltages from the transformer and provides five regulated dc voltages for use by the CPU, Front Panel assembly, Rear Panel assembly, and the cooling fans. All power supply voltages are referenced to COMMON, which is the transformer center tap for the ±12V supplies. Test points at the top of the assembly can be used to check unregulated input voltages, and regulated dc output voltages. Table 2-2 lists the supplies generated by the Digital Power Supply.

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