85RF Fluke Electronics, 85RF Datasheet - Page 57
85RF
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
As the read period begins, the INTEG switches open and the READ switches
close. This applies the known reference voltage from a “flying” capacitor
whose polarity is chosen by the a/d converter to be the opposite of the
polarity of the unknown input voltage. The INTEG capacitor begins
discharging at a fixed rate while a counter begins counting. The counting
stops counting when the INTEG capacitor voltage equals the initial autozero
voltage. The count is proportional to the unknown input voltage, and is
placed on the display by the microcomputer.
If during the read period the counter counts up to the maximum number of
counts for a full-scale reading (19999 counts) and the INTEG capacitor
charge has not yet reached the initial autozero voltage, the microcomputer
knows an overrange reading has been taken. The microcomputer places
“OL” on the display and commands the a/d converter to go into the overload
(OL) period which rapidly slews the integrator voltage back to the initial
autozero voltage.
The measurement cycle ends at the end of the read period for an on-scale
reading, or at the end of the overload period for an overrange reading. A new
measurement cycle then begins with the autozero period. The display update
rate for measurement functions that use the a/d converter is approximately
0.4s, or about 2-1/2 readings per second.
Waveform at
the Integ
Capacitor
Figure 3-3. A/D Measurement Cycle
Accumulated Counts
AZ
A/D Measurement Cycle
400 ms
Integ
100 ms
Read
Overrange (“OL” on display)
Functional Description
Theory of Operation
Fullscale reading
OL
1
/
AZ
2
scale reading
dy27f.eps
3
3-7