Keithley 6514 User Manual

6-6 Range, Units, Digits, Rate, and Filters
Rate
The RATE key selects the integration time of the A/D converter. This is the period of time the
input signal is measured. The integration time affects the amount of reading noise, as well as the
ultimate reading rate of the instrument. The integration time is specified in parameters based on
a number of power line cycles (NPLC), where 1 PLC for 60Hz is 16.67msec (1/60) and 1 PLC
for 50Hz (and 400Hz) is 20msec (1/50).
In general, Model 6514 has a parabola-like shape for its speed vs. noise characteristics and is
shown in Figure 6-1. Model 6514 is optimized for the 1 PLC to 10 PLC reading rate. At these
speeds (lowest noise region in the graph), Model 6514 will make corrections for its own internal
drift and still be fast enough to settle a step response <100ms.
The rate setting is global for all measurement functions. Therefore, it does not matter what
function is presently selected when you set rate.
There are two ways to set rate. You can select slow, medium, or fast by using the RATE key,
or you can set the number of power cycles from the NPLC menu that is accessed by pressing
SHIFT and then NPLC.
Rate Key — The RATE key selections are explained as follows:
• SLOW — Selects the slowest front panel integration time (6 PLC for 60 Hz or 5 PLC
for 50 Hz) and sets display resolution to 5½-digit resolution. The SLOW rate provides
better noise performance at the expense of speed.
• MED — Selects the medium integration time (1 PLC) and sets display resolution to
5½-digit resolution. Select the MED rate when a compromise between noise perfor-
mance and speed is acceptable.
•FAST — Selects the fastest front panel integration time (0.1 PLC) and sets display res-
olution to 4½-digit resolution. Select the FAST rate if speed is of primary importance (at
the expense of increased reading noise).
To change the rate setting, press (and release) the RATE key until the desired rate annunciator
(SLOW, MED or FAST) is displayed.
Lowest
noise
region
Voltage
Noise
166.7µs 16.67ms 166.67ms
Integration Time
Figure 6-1
Speed vs. noise
characteristics

Keithley 6514 Specifications

General

Brand	Keithley
Model	6514
Category	Measuring Instruments
Language	English