85RF Fluke Electronics, 85RF Datasheet - Page 55

• Manufacturer Part Number: 85RF
• Description: PROBE HIGH FREQ 500MHZ
• Manufacturer: Fluke Electronics
• Type: High Frequencyr

Specifications of 85RF

• Impedance: 10M Ohm
• Voltage - Max: 30VRMS, 200VDC
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption
• Ratings: -
• Current Rating: -
• Color: -
• Termination: -
• Wire Insulation Material: -
• Cable Length: -
• Other names: 532457

2.
3.
4.
After the results are displayed, the routine begins again at the first step.
3-4.
A block diagram of the MAC is shown in Figure 3-1. The digital control
logic includes a buffer and decoder, read and write logic, status and control
registers, and logic control for the continuity function. The power supply
control uses the calibrated 1.0000V a/d reference voltage obtained from a
bandgap reference diode to regulate the 5.2V main power supply for the
instrument. When the continuity function is selected and continuity is
detected, the MAC generates the tone by supplying a square wave to the
external piezoelectic transducer.
3-5.
The heart of the MAC is the dual-slope a/d converter. A block diagram of the
analog portion of the a/d converter is shown in Figure 3-2. The internal
buffer, integrator, and comparators work in conjunction with external
resistors and capacitors to convert the dc analog voltage to a digital number.
The internal switches are FET switches that are controlled by the
microcomputer and the MAC digital control logic. The switchable integrator
gain depends of the function and range selected.
The complete a/d measurement cycle is shown in Figure 3-3. It consists of
three consecutive time periods: autozero (AZ), integrate (INTEG) and read.
A fourth time period, overload (OL) is also used if an overrange reading is
taken. The total length of the measurement cycle is 400 ms. The length of the
integrate period is fixed at 100 ms. One hundred ms is a multiple of the
period of 50 Hz or 60 Hz power, which helps to reduce the possible power
line noise that might interfere with the measurement. The waveform at the
INTEG capacitor is shown for three sample measurement readings: half-
scale, full-scale, and overrange.
The microcomputer initiates the a/d measurement cycle (approximately
400 ms) which is described later in this chapter.
The microcomputer processes the data obtained in the measurement
cycle. This includes calculations for the relative (REL) offset and M
autoranging.
The microcomputer displays the results. The results remain on the
display until it is updated.
Measurement Acquisition Chip (MAC)
A/D Converter Cycle
Functional Description
Theory of Operation
3
3-5