Page 8
4.7
Throughput
Throughput is a measure of how fast the instrument processes data. The rate at which the instrument acquires data is a
function of the ―Gate Time‖ and the input frequency. The instrument gets a start pulse then it continues to get pulses until
the Gate Time elapses. The next pulse ends this measurement and starts the next. At frequencies slower than the Gate Time,
the update rate is equal to the period of the input frequency. Eventually, the instrument has to make the decision that the
input is zero, because theoretically it could wait forever for the next pulse. This Low-End timeout is programmable.
4.7.1
Display Update Rate
Although the instrument can update up to 244 times a second, to display the data at this rate would result in a totally
erratic display. Therefore, the instrument limits the display update rate to once every ½ second. Obviously if the input
pulses are spaced more than ½ second apart, the instrument will not have any new data until the next pulse comes
along, and the time to update will be greater than ½ second. The point at which the update rate becomes longer than
every ½ second is when the period of the input (time between pulses) is greater than ½ second, which is 2 Hz or 120
RPM. Thus, for an input greater than 2 Hz or 120 RPM, the update rate is twice a second.
For very fast inputs, the unit averages the readings between display updates so that the value displayed is an average of
the total number of acquisitions since the last update.
4.7.2
Internal Update Rate - GATE
The rate at which the limits are checked, the analog output is updated, and the minimum and maximum are updated, is
at the maximum rate at which the instrument acquires data. This is set by the
GATE
menu item. The Gate Time can be
set to 32.786 mSecs (
STD
) or 4.096 mSecs (
FAST
The
STD
setting is slower (up to 31 readings per second) but gives more accurate readings especially for the maximum
and minimum readings. Below 31 Hz or 1860 RPM, the internal update rate is the period of the input frequency. Thus,
the response of the alarms, etc can be seen to be a function of the input. Above an input of 31 Hz, the alarms respond
within 66 milliseconds. Below this input they respond within (1
input frequency) seconds.
The
FAST
gate time is faster (up to 244 readings per second) but is less accurate (about 0.025% of reading worst case
at high frequencies). Below 244 Hz or 14,640 RPM, the internal update rate is the period of the input frequency. Thus,
the response of the alarms, etc can be seen to be a function of the input. Above an input of 244 Hz, the alarms respond
within 9 milliseconds. Below this input they respond within (1
input frequency) seconds.
At input frequencies below 31 Hz or 1860 RPM there will be no difference in the two settings.
The instrument has a special feature to allow it to quickly respond to rapid deceleration and still measure down to 5
RPM with 1 pulse per revolution. (To measure to 1 RPM, 5 pulses per revolution are required). After receiving no
input pulses for about 67 milliseconds for the Standard gate mode or 37 mSecs for the Fast gate mode, the instrument
will calculate a reading as though an input pulse had just occurred. If this new reading is less than the last reading, the
instrument uses it. Until an input pulse is detected or the Low-End timeout is reached, the instrument will ―force‖
another reading every 33 milliseconds. These ―forced‖ readings will update the analog output, limits, and the max/min.
The last ―forced‖ reading of every ½ second will be displayed every ½ second. The Low-End timeout can be set to 12,
1 or 0.5 seconds. Refer to
4.7.3
Low End
Low End is applicable to
RPM
,
FREQ
,
SCALE
, and
SECAP
Modes only. Low End selects how many seconds may
elapse between input pulses before the unit displays the reading zero. There is a tradeoff between the lowest reading
available and how quickly the unit responds when the input pulses stop and displays 0. There are three values: 12
seconds, 1 second, and 1/2 seconds. In the RPM mode, with one pulse per revolution, these settings correspond to the
lowest RPM reading of 5, 60 and 120 RPM respectively.
4.8
PULSE OUTPUT
The Pulse Repeater Output provides a conditioned TTL positive going 5 V pulse out for each pulse in. The sense of the
output, high pulse or low pulse, is programmable by the user. See
Section 5.9
.
5.0
USING THE MENU
To enter the
MENU Mode
, press the
SET
button. The display will show the first top-level menu item, which is
for
Channel 1 setup. Continuing to press the
SET
button will cycle through all options and show the current settings. At any point
press the
RECALL
button to back out (
) the current setting. Pressing
RECALL
again will eventually exit from the Menu.
Once in the MENU Mode, with
displayed, press the
UP
or
DOWN
buttons to cycle through the top-level menu
options.
The top-level menu choices are:
Channel 1
- Set up parameters for Channel 1 – the primary input Channel
Channel 2
- Set up parameters for Channel 2 – the Auxiliary Input Channel
