Monarch Instrument ACT-3 - Manual (Page 5)

6.12 BAUD (Baud Rate) ......................................................................... 13
6.13 LOEND (Low End) .......................................................................... 13
6.14 GATE (Measurement Rates) .......................................................... 13
6.15 DIAG (Self Test) .............................................................................. 13
7.0 PULSE OUTPUT ....................................................................................... 14
8.0 SERIAL OUTPUT ...................................................................................... 14
8.1 Data from the RS232C Interface ................................................... 14
8.2 RS232C Commands ....................................................................... 15
8.3 Run Mode Commands ................................................................... 15
8.4 Control Commands ....................................................................... 16
9.0 OPTIONS and ACCESSORIES / SENSORS ............................................ 18
APPENDIX A - SCALING THE ACT FOR ENGINEERING DISPLAYS ................ 19
APPENDIX B - SOME USEFUL CONVERSIONS ............................................... 22
APPENDIX C - USING THE SINGLE EVENT CAPTURE MODE ......................... 23
APPENDIX D - ACT3 RS232C INTERFACE CONNECTIONS .............................. 24
MEASUREMENT MODE BUTTON OVERVIEW .................................................. 25
MENU OVERVIEW ............................................................................................. 26
23
APPENDIX C – USING THE SINGLE EVENT CAPTURE MODE
This is to how to calculate a scale factor and to show sources of measurement error.
In this example, the distance between sensors is 1 inch and we want the readings displayed in Miles Per
Hour (MPH). The fastest measurement we intend to make is 130 MPH.
First calculate the scale factor. With a scale of one, the tachometer will display readings in pulses per
second.
The scale factor can be calculated as:
1 Pulse 1 Inch 3600 Seconds 1 Foot 1 Mile 0.05681818 Miles
——— x ——— x —————— x ———— x ———— = ————————
Second
Pulse Hour 12 Inches 5280 Feet Hour
There will be an error because scale factors can only be five digits. Therefore, the scale factor is
rounded to 0.0568.
You will also have an error in the placement of the sensors. The tape edges won’t be exactly 1 inch
apart. Assuming the edges were really 1.01 inches apart there would be 1% error. So at 130 MPH your
reading would be 128.7 MPH.
The internal clock inside the tachometer runs at 2 MHz. All measurements are synchronized to this
internal clock giving a ±0.5 microsecond uncertainty. As RPM, MPH, etc increase, the measurement
time decreases. As the measurement time decreases, the small measurement uncertainty becomes a
larger percentage of the measurement.
At 130 MPH there would be 0.00043706293706 seconds between pulses. (Seconds = scale factor /
130 MPH.) This is equal to about 874 clock cycles for a 2 MHz internal reference clock.
873 clock cycles = 130.16766 MPH
875 clock cycles = 129.87013 MPH
Therefore, we have an error of ±0.148765 MPH from the clock resolution at 130 MPH. The sensors
must be placed further apart for better resolution.
Accuracy Specification
Measuring only one rotation or linear motion measurement (just a start pulse and a stop pulse)
RPM SECS 2Mhz CLOCKS ± % ± RPM ± RPM Displayed
5 12 24,000,000 8.333e-6 4.1665e- 7 0.0001
50 1.2 2,400,000 8.333e-5 4.1665e-5 0.001
500 1.2e-1 240,000 8.333e-4 4.1665e-3 0.01
5,000 1.2e-2 24,000 8.333e-3 4.1665e-1 0.5
50,000 1.2e-32 2,400 8.333e-2 41.665 42
100,000 6e-4 1,200 1.6e-1 160 160
500,000 1.2e-4 240 8.33e-1 4166 4166