ProbeScope V3.0 for Windows/DOS (220-0310) Operation - Part 2 Faxback Doc. # 33360 INSTANTANEOUS AC VOLTAGE MEASUREMENTS You can use the ProbeScope to measure an AC signal's instantaneous voltage at any given point on the signal waveform or an AC signal's midpoint as it is raised or lowered by a DC bias voltage. You can make this type of measurement in much the same way as you make AC peak-to-peak measurements. 1. Set the input coupling switch to GND. 2. Using the zero line adjustment, vertically position the trace to a convenient line on the grid overlay. NOTE: The position on the grid overlay depends on the polarity and amplitude of the input signal, but should be chosen so the trace lies along one of the major divisions on the grid overlay. If the trace is widened by stray interference, ground the probe body near the point being measured. The trace position is the voltage reference line and all voltage measurements are read in respect to this line. (Do not adjust the vertical positioning control after the reference is established.) 3. If it was necessary to ground the tip (see Step 2 note), remove the tip from the tip from the ground or reference voltage. This readies the tip so you can use it to make a measurement. 4. Set the input coupling switch to DC. 5. Connect the probe end of the ground wire to the probe's GROUND (0 VOLT) jack and the alligator clip end to the signal source's ground reference. 6. Click on the horizontal cursor icon to display the horizontal cursors. 7. Apply the probe tip to the signal source, then click on the oscilloscope hold icon. 8. Measure the vertical distance between a desired point on the waveform and the reference line as follows: a. Place the mouse cursor directly over the oscilloscope screen's lower horizontal cursor. The cursor's shape changes to a cross. b. While you press and hold the left mouse button, move the mouse up or down until the screen's lower horizontal cursor touches the reference line. c. Place the mouse cursor directly over the oscilloscope screen's upper horizontal cursor. The cursor's shape changes to a cross. d. While you press and hold the left mouse button, move the mouse up or down until you place the screen's upper horizontal cursor on the desired point on the waveform. a= If you place the screen's upper horizontal cursor anywhere along the waveform except the midpoint between the peaks, the measurement equals the instantaneous AC voltage. b= If you place the screen's upper horizontal cursor directly on the midpoint between the peaks, the measurement equals the DC bias. The /\ VOLT: box shows the instantaneous voltage level of the AC signal at the measured point, or the voltage level of the midpoint of an AC signal after being raised or lowered by the DC bias voltage. NOTES: If the /\ VOLT: box does not appear on the monitor, click on the DVM icon. You can also calculate the approximate voltage levels by multiplying the approximate distance by the deflection factor. FREQUENCY MEASUREMENTS Since frequency and time are reciprocals of each other, when you know one (frequency or time), you can easily solve for the other (f= 1/t, then t= 1/f). Therefore, if you measure the time period of a recurrent waveform as 0.2 us, the frequency is 5 MHz (or 1/0.2 us). NOTE: Since a DC voltage does not have a frequency, you cannot make frequency measurements on a DC voltage. 1. Set the input coupling switch to GND. 2. Using the zero line adjustment, vertically center the trace on the grid overlay. NOTE: If the trace is widened by stray interference, ground the probe body near the point being measured. The trace position is the voltage reference line and all voltage measurements are read in respect to this line. (Do not adjust the vertical positioning control after the reference is established.) 3. If it was necessary to ground the tip (see Step 2 note), remove the tip from the ground or reference voltage. This readies the tip so you can use it to make a measurement. 4. Set the input coupling switch to AC. 5. Connect the probe end of the ground wire to the probe's GROUND (0 volt) jack and the alligator clip end to the signal source's ground reference. 6. Click on the vertical cursor icon to display the horizontal cursors. 7. Apply the probe tip to the signal source, then click on the oscilloscope hold icon. 8. Measure the horizontal distance between rising or falling points on the displayed waveform as follows: a. Place the mouse cursor directly over the oscilloscope screen's left vertical cursor. The cursor's shape changes to a cross. b. While you press and hold the left mouse button, move the mouse left or right until the screen's left vertical cursor touches a point where the rising or falling edge of the waveform intersects with the zero reference line. c. Place the mouse cursor directly over the oscilloscope screen's right vertical cursor. The cursor's shape changes to a cross. d. While you press and hold the left mouse button, move the mouse left or right until the screen's right vertical cursor touches the next point where the waveform's rising or falling edge intersects with the zero reference line. NOTE: To avoid inaccurate frequency measurements, make sure you set the cursors in Steps b and d to two consecutive rising or two consecutive falling points of a displayed waveform. The frequency measurement will be inaccurate if you set one vertical cursor to a rising edge and the other to a falling edge. e. The /\ TIME IN box shows the actual frequency in HERTZ or SECONDS. NOTES: You can click the button on the tool bar to toggle between HERTZ or SECONDS. The timebase on the computer's TIMEBASE display changes with the grid overlay settings. When measuring a waveform: a. If the either the time or frequency is known, simply calculate the reciprocal of the known value to figure the unknown value. b. Start with the smallest selectable timebase on the ProbeScope (50 ns) and increase it one step at a time (100 ns, 0.5 us, 1 us, 5 us, 10 use, 50 us, 0.1 ms, 0.5 ms, or 1 ms) until the displayed signal shows one of two complete cycles of a waveform. FREQUENCY MEASURING LIMITS: You must have a minimum of one complete cycle of a waveform on the display. You cannot have more than one cycle per division. PHASE MEASUREMENTS You can compare two signal waveforms of the same frequency either from two separate points on the same electronic device, or from similar points on two separate electronic devices. The phase difference between the two signal waveforms is measured in degrees. NOTE: You must calculate the number of degrees per division for this measurement to work with your ProbeScope. GRID OVERLAY DEGREE CALCULATION Since a complete cycle of a sine wave is 360 degrees, it is easy to calibrate the grid overlay in degrees. For example, if the ProbeScope's controls are adjusted so one cycle of the input waveform spans 9 squares on the grid, then each square represents 40 degrees of the complete cycle (360/9=40). The grid display is then considered to be calibrated to 40 degrees per square. MEASURING PHASE Follow these steps to measure the phase difference between two signals. 1. Set the input coupling switch to GND. 2. Using the zero line adjustment, vertically center the trace on the grid overlay. NOTE: If the trace is widened by stray interference, ground the probe body near the point being measured. The trace position is the voltage reference line and all voltage measurements are read in respect to this line. (Do not adjust the vertical positioning control after the reference is established.) 3. If it was necessary to ground the tip (see Step 2 note), remove the tip from the ground or reference voltage. This readies the tip so you can use it to make a measurement. 4. Set the input coupling switch to AC. 5. Connect the probe end of the ground wire to the ProbeScope's GROUND (o VOLT) jack and the alligator clip end to the first signal source's ground reference. 6. Click on the vertical cursor icon to display the horizontal cursors. 7. Apply the ProbeScope's tip to the first signal source, then click on the oscilloscope hold icon. 8. Measure the signal level and slope of the first circuit as follows: a. Place the mouse cursor directly over the oscilloscope screen's left vertical cursor. The cursor's shape changes to a cross. b. While you press and hold the left mouse button, move the mouse left or right until the screen's left vertical cursor touches a point where the rising or falling edge of the first waveform intersects with the zero reference line. 9. If the second signal source to be measured id a separate circuit on the same electronic device, simply remove the ProbeScope's tip from the first circuit's signal source and apply it to the next circuit's signal source. If the second signal source to be measured is a separate electronic device: a. Remove the alligator clip on the ground wire and the probe's tip from the first signal source's ground and signal references. b. Connect the alligator clip on the ground wire to the second signal source's ground reference. c. Apply the ProbeScope's tip to the second signal source's circuit to be measured. 10. Measure the signal level and slope of the second circuit as follows: a. Place the mouse cursor directly over the oscilloscope screen's right vertical cursor. The cursor's shape changes to a cross. b. While you press and hold the left mouse button, move the mouse left or right until the screen's right vertical cursor touches a point where the rising or falling edge of the second waveform intersects with the zero reference line. 11. Measure the displacement (number of horizontal squares) between corresponding points on the measured signals and calculate the number of degrees per division (see "Grid Overlay Degree Calculation). NOTE: To avoid inaccurate phase measurements, make sure you set the cursors in Steps 6b and 10b to two corresponding rising or two corresponding falling points on the displayed waveforms. The phase measurement will be inaccurate if you set one vertical cursor to a rising edge and the other to a falling edge. The /\ TIME IN box shows the single cycle frequency in HERTZ or SECONDS. NOTE: If the value shown in the /\ TIME IN box is in HERTZ, click the tool bar button to toggle to SECONDS. 12. Divide the displacement (the value shown in the /\ TIME IN box) by the value in the timebase (time-per-division), then multiply the result by the number of degrees per division calculated in Step 11. NOTE: The relative amplitude of the measured signals does not affect the phase measurement if the signals are centered around the grid's center horizontal line. SINGLE SWEEP WAVEFORM MEASUREMENTS You can measure a waveform that occurs only once without repeating, such as a noise spike that occurs when you turn on an electronic device. Follow these steps to measure a single sweep waveform. 1. Set the zero reference line along the second or third line on the grid overlay. 2. Continuously press the menu button until the trigger mode appears on the display. 3. Press the select button to set the trigger mode to: + EXTERN (if you want to trigger on the incoming signal's rising edge), or - EXTERN (if you want to trigger on the incoming signal's falling edge). 4. Press the menu button so TRIGGER LEVEL appears on the ProbeScope's display. 5. Continuously press the select button until you set the trigger level as desired. NOTE: The trigger level you select sets the level of the incoming waveform that causes the ProbeScope to begin reading the signal 6. Press the menu button until the mode screen appears on the ProbeScope's display. 7. Press the select button so SINGLE appears on the ProbeScope's display. 8. Press the menu button so WAITING appears on the ProbeScope's display. 9. Set the input coupling switch to GND. 10. Using the zero line adjustment, vertically position the trace to a convenient line on the grid overlay. NOTE: If the trace is widened by stray interference, ground the probe body near the point being measured. The trace position is the voltage reference line and all voltage measurements are read in respect to this line. (Do not adjust the vertical positioning control after the reference is established.) 11. If it was necessary to ground the tip (see Step 10 note), remove the tip from the ground or reference voltage. This readies the tip so you can use it to make a measurement. 12. Set the input coupling switch to AC. 13. Apply the probe tip to the signal source to be measured. 14. Turn on the device to be measured. A single waveform appears on the oscilloscope screen. 15. Measure the single sweep frequency as follows: a. Place the mouse cursor directly over the oscilloscope screen's left vertical cursor. The cursor's shape changes to a cross. b. While you press and hold the left mouse button, move the mouse left or right until the screen's left vertical cursor touches the point where the rising edge of the waveform intersects the zero reference line. c. Set the computer's mouse cursor directly over the oscilloscope's screens' right vertical cursor. The cursor's shape changes to a cross. d. While you press and hold the left mouse button, move the mouse left or right until the screen's right vertical cursor touches the point where the next rising edge of the waveform intersects the zero reference line. 16. The /\ TIME IN box shows the single cycle frequency in HERTZ or SECONDS. NOTE: You can click the tool bar button to toggle between HERTZ or SECONDS. USING THE DVM The following applications describe how to make basic voltage measurements using the ProbeScope's digital voltmeter (DVM) mode. These applications are not described in detail, but are designed to familiarize you with basic DVM operating techniques. In digital voltmeter measurements, the measured AC or DC voltage is converted to digital values using an analog-to-digital (A/D) converter. In the AC mode, the ProbeScope rectifies the AC signal to convert it to DC. The DC is then converted to a digital value by a 6-bit resolution A/D converter, then multiplied by 0.707 to display the RMS value. You must have at least two cycles of a waveform for the ProbeScope to accurately measure AC DVM values. NOTE: The voltmeter function is to be used only for pure AC and DC measurements. Only sine waves are allowed for AC measurements since the ProbeScope does not support true RMS functions. For measuring an AC signal on a DC bias, use the oscilloscope (see "Using the Oscilloscope"). In the DC mode, the DC is directly converted to a digital value by the 6- bit resolution A/D converter. An average of up to 128 recorded values appears on the screen. A negative value is displayed when the average is below the reference line. Follow these steps to measure a signal's voltage level. 1. Continuously press the menu button until the FUNCTION mode appears on the display. 2. Press the select button to set the function mode to DVM, the press the menu button again. 3. Set the input coupling switch to GND. 4. Connect the probe end of the ground wire to the ProbeScope's GROUND (0 Volt) jack and the alligator clip end to the first signal source's ground reference. 5. Using the zero line adjustment, vertically position the trace to a convenient line on the grid overlay. CAUTION: To avoid an overload when measuring AC, make sure the zero line is centered vertically on the grid overlay. NOTE: If the trace is widened by stray interference, ground the probe body near the point being measured. The trace position is the voltage reference line and all voltage measurements are read in respect to this line. (Do not adjust the vertical positioning control after the reference is established.) 6. If it was necessary to ground the tip (see Step 6 note), remove the tip from the ground or reference voltage. This readies the tip so you can use it to make a measurement. 7. Set the input coupling selector to AC or DC (depending on the voltage you want to measure). 8. Set the input voltage range to the appropriate 1V, 10V, or 100V range scale. CAUTIONS: Always set the selector to the highest range when you are not sure of the voltage to be measured. Never exceed 100 Volts AC (peak-to-peak) or DC between the measured test point and ground. The maximum AC RMS measurement is (Voltage Range Selection / 2) x 0.707. 9. Click on the icon on the tool bar to display the DVM box. 10. Apply the probe tip to the circuit to be tested. The actual voltage appears on the ProbeScope's display and on the monitor's DVM box. If you want to freeze the current voltage reading so you can take another measurement reading for comparison, click on the HOLD DVM button on the tool bar. (yo/all-06/13/96)