Measuring Functions - Hameg Instruments HM8122 Manuel

Definitions
Relative Error
The inaccuracy (relative error = RE) of a measurement
depends on 4 factors:
– rel. resolution
– rel. trigger error (if any)
– rel. time base error (if any)
– rel. systematic error (if any)
RE = ± (rel. resolution + rel. time base error
+ rel. trigger error + rel. systematic error)
Trigger error (TE)
Trigger error is the absolute measurement error due to
input noise, causing triggering which is too early or too late
TE at FREQUENCY, PERIOD, RATIO
TE = ± Total Noise voltage (RMS): Signal slew rate (V/s)
TE = ± 1/Freq x Pi X S/N-ratio (sine wave)
TE at TIME INTERVAL A-B, PULSE WIDTH
TE = ± Total Noise Voltage /Slew rate (at start point)
± Total Noise Voltage /Slew rate (at stop point)
* Total Noise Voltage = Square root of (trigger noise) E2
+ (signal noise at trigger point) E2
Resolution
Multiple events measurements
At FREQUENCY, PERIOD, RATIO, the resolution is the
smallest increment between two measuring results. The
measuring resolution is due to the ±1 count error. After
calculation, the result to be displayed is truncated to
include only significant digits giving a measuring resolution
of 0.2 .. 2 LSD units. Total resolution, including LSD
resolution, is therefore 1 LSD unit or 2 LSD units but can
always be reduced to 1 LSD unit by increasing the
measuring time somewhat.
Single event measurements
The resolution is one clock pulse period, regardless of the
measuring time.
Systematic error: <4ns (for time interval)
Time Base Error (TBE)
The relative time base error is the relative deviation of the
clock pulse frequency from 10 MHz.
Rel. TBE = ∆ f/10 MHz.

Measuring Functions

FREQ. C: Sets the instrument to measure the frequency
of the signal connected to input C.
TOTL. A: The counter will totalize events (pulses or
cycles) on input A. Measurement stops and
display freezes as soon as the input signal is
removed or DISPLAY HOLD is depressed.
Depressing RESET during totalizing clears the
display and starts a new measurement when
releasing the button. Reset is active as long as
the switch (21) is depressed. When connecting
the TRIGGER B output (38) at the rear panel to
EXTERNAL GATE input (40), and at the same
time applying a "gate signal" to the B input,
Totalizing A during B is performed as soon
the EXTERNAL GATE mode (7) is selected.
22 HM8122
Totalizing A during External Gate is performed applying
a TTL signal to the Ext. Gate Input (40).
Per. A: Sets the counter to measure the period
duration of the signal connected to input A.
Freq. A: same as Freq. C
Freq. B: same as Freq. C
Ratio A/B: Sets the counter to measure the frequency
ratio between the signals connected to
channels A and B. The higher frequency should
be always applied to channel A, to achieve the
highest resolution possible.
TI AVG.: Sets the counter to measure the average
Time Interval between events on channels A
and B during a measuring cycle.
TI A to B: Like TI AVG. with only one interval measured.
Resolution is 10 ns.
RPM: Sets the counter to measure the number of
revolutions per minute. The result is displayed
without dimension.
The number of pulses per revolution (NPR) is
preselectable up to 65535 (default = 1).
Installation
Before connecting the instrument to the line, ensure that
it is set to the local line voltage. On delivery the counter is
set to either 110 V or 220 V, as indicated on the line voltage
selector on the rear panel.
If the voltage setting is incorrect, set the line voltage
selector in accordance with the local voltage before
connecting the instrument to the line.
The counter is protected by a primary fuse and a thermal
fuse inside the mains transformer. The primary fuse has
to be changed when the mains voltage setting is changed.
For 220 V use a 0.315 A delayed action fuse and for 110
V use a 0.63 A delayed action fuse. Remove the line plug
before fitting a fuse. Ensure that only fuses of the specified
type are used.
Power switch
In position power off (St.By) only the supply voltages for
the logic circuits and the analog inputs are switched off.
The power supply for the oven oscillator is still connected.
The "Stand By"-mode is indicated by two vertical segments
lit in the leftmost digit.
Warning! This is a secondary power switch. Also in
off position there will be live parts inside the
instrument. To separate the instrument completely
from the mains, the mains cable must be discon-
nected.
Power-on test
When the installations for local line voltage have been
made, switch the power on. Now a practical test of the
correct operation of the HM 8122 is run automatically.
This self check programm starts every time power is
switched from ST.by to on.
As soon as power is applied, the display shows type and
version of the actual instrument and the GATE indicator
appears.
Then the first display is replaced by the date of the last
calibration. While the date appears all LEDs are lit and the
eprom and all functions of the counter are tested.
Subject to change without notice