HP 3457A Service Manual page 168

8-3. STATIC HANDLING
Static electricity is a familiar phenomenon which, except for an occasional shock, doesn't seem very
serious. It has been proven in the electronics industry: however, that electrostatic discharge (ESD) is a
major cause of component failure. In many cases, the component damaged may not fail immediately
but cause poor instrument reliability and additional repairs at a later date. ESD damage can occur at
static levels too low for human perception. It has been shown that ESD can affect both active and pas-
sive devices.
The following guidelines are the minimum requirements for a static-safe service environment:
¢ The work bench must be equipped with a conductive table mat. The mat should be con-
nected to earth ground through a | Mohm resistor. The mat must be equipped with at least
one connection for connecting wrist straps.
e All persons who handle and service the instrument must wear a conductive wrist strap in
contact with bare skin. This wrist strap must be connected to the conductive table mat.
e All metal equipment at the work station must be grounded to earth ground. This includes
soldering irons, desoldering tools, shelving, and equipment stands.
© Only one common ground can be provided at a work station,
© The work station must be kept free of nonconductive items such as common plastics, poly
bags, cardboard, cigarette or candy wrappers. There must be no rugs or carpet on the floor,
shelving or bench top.
© Proper containers must be used for shipping, storing and transporting assemblies.
8-4. RECOMMENDED TEST EQUIPMENT
Equipment to test and repair the HP 3457A is listed in Section | (Table 1-3) of this manual,
8-5. GENERAL BLOCK DIAGRAM THEORY OF OPERATION
The HP 3457A is a versatile, high precision digital multimeter capable of measuring AC or DC volts, AC
or DC current, AC+DC volts or current, resistance, frequency, and period. It measures voltages up to
300 VAC or 300 VDC with high DC resolution and accuracy. Reading rates greater than 1000 readings
per second can be achieved.
The following paragraphs provide a simplified explanation of the HP 3457A circuit operation. Refer to
the simplified block diagram in Figure 8-1 for the following description.
The HP 3457A can be divided into two basic sections, the Chassis Common Circuitry and the Floating
(isolated) Common Circuitry. The Chassis Common Circuitry provides instrument control and com-
munication with other instruments, through the HP-IB, or the user through the front panel keyboard
and display. The Floating Common Circuitry is responsible for converting the analog input signals to
digital information. The two sections communicate with each other through the Isolation Logic
Circuitry.
HP 3457A Multimeter
8-2