Exercise 2: FACET Base Unit Familiarization

Transcription

1 Exercise 2: FACET Base Unit Familiarization EXERCISE OBJECTIVE When you have completed this exercise, you will discover the operating features of the base unit and DC FUNDAMENTALS circuit board. You will verify your results with an operational test. DISCUSSION REFER TO YOUR BASE UNIT The base unit contains CM and fault toggle switches, power supply controls, LEDs, and a Zero Insertion Force (ZIF) connector that accepts circuit boards. Faults toggle switches CM toggle switches Zero Insertion Force (ZIF) connector Power is applied to the base unit when the AC cord is plugged in and the power switch is on. The base unit s power switch should be in the off position when inserting circuit boards. Power switch On the base unit are LEDs (light-emitting diodes) indicating the presence of the plus and minus 15 Vdc internal supplies. The LEDs are located above the control knobs of the negative and positive variable suplies. When power is applied to the base unit, the LEDs illuminate. One or both LEDs will be off should a base unit protective circuit activate (to crowbar the base unit s power source). 14 FACET by Lab-Volt

2 DC Fundamenatals Trainer Familiarization To remove the crowbar condition on a base unit, turn off the POWER switch on the base unit, correct the problem, and turn the POWER switch on. If you cannot solve the problem, ask your instructor for help. One of the base unit LEDs is off (the other is on). This condition indicates a. the base unit s power switch is off. b. the circuit board is not inserted. c. the wrong circuit board is inserted. d. an overvoltage and/or short circuit condition on a circuit board. Each of the internal variable power supplies are adjusted with COARSE and FINE knobs (concentric shaft) located on either end of the base unit. Coarse Fine The left controls adjust the negative variable supply between 0 Vdc and -10 Vdc. The right controls adjust the positive variable supply between 0 Vdc and +10 Vdc. There are twenty CM toggle switches, numbered 1 through 20, in the base unit. When a CM switch is in Variable 0 to 10 Vdc power source Variable 0 to +10 Vdc power source There are twelve computer-controlled fault relays in the base unit. Each fault, when the corresponding switch is toggled, inserts a malfunction in a selected circuit located on the circuit board. The tolerances of acceptable answers in this course are based on an accuracy of these voltages to within 3 (0.45 Vdc). To insert your circuit board into the base unit, a. ensure that the ZIF connector is open and the power switch is off. b. ensure that the ZIF connector is closed. c. use excessive force and don t check the position of the ZIF connector. To remove your circuit board from the base unit, a. ensure that the power switch is off and the ZIF connector is open. b. ensure that the ZIF connector is closed. c. use excessive force and don t check the position of the ZIF connector. FACET by Lab-Volt 15

3 Proper electrical connections between the base unit and a circuit board require that the ZIF connector be a. open. b. closed. c. either open or closed. PROCEDURE Locate the OHM S LAW circuit block on the DC FUNDAMENTALS circuit board. Do not use a two-post connector to complete the circuit. Select the dc volts function on your multimeter, and connect test leads to the meter to measure voltage. NOTE: Place the black test lead to the meter common terminal and place the red test lead to the meter volts (or Vdc) input terminal. Connect your multimeter across the variable power source. Place the red test lead at the top and the black lead at the bottom. NOTE: If your test leads have alligator connectors, insert a terminal post into the OHM S LAW circuit block connectors and attach your alligator leads to the posts. 16 FACET by Lab-Volt

4 DC Fundamenatals Trainer Familiarization Which variable power supply control(s) do you use to initially adjust the OHM S LAW circuit block voltage? a. the positive FINE base unit control. b. the positive COARSE and FINE base unit controls. c. the negative FINE base unit control. d. the negative COARSE and FINE base units controls. Use the positive COARSE and FINE controls to adjust the circuit voltage to 10.0 Vdc. Note how the FINE control allows a precise voltage adjustment. Set the FINE control to its approximate midpoint. Adjust the COARSE control for a voltage reading of about 5 Vdc. Use the FINE control to set a precise circuit voltage of 5.00 Vdc (on an analog meter, ensure that your reading is about 5 Vdc). Which procedure allows you to set a circuit voltage precisely? a. First set the FINE control to the approximate voltage. Then use the COARSE control to determine the precise circuit voltage. b. First set the COARSE control to the approximate voltage. Then use the FINE control to determine the precise circuit voltage. Remove all circuit board connections. CONCLUSION The base unit power switch must be off, and ZIF connector must be opened before a circuit board can be inserted into the base unit. The base unit ZIF connector must be closed before the power switch is turned on to establish the proper circuit paths between base unit and circuit board. The COARSE and FINE controls of the base unit variable power supplies are used to set a precise circuit board voltage. REVIEW QUESTIONS 1. To change the value of the positive power source in the OHM S LAW circuit block from 6.00 Vdc to 6.08 Vdc, the a. positive variable COARSE control is used. b. positive variable COARSE and FINE controls are used. c. positive variable FINE control is used. d. positive power source cannot be changed. 2. The variable power source on the OHM S LAW circuit block of the DC FUNDAMENTALS circuit board is controlled by the a. positive supply controls. b. position of the ZIF connector. c. negative supply controls. d. by the resistor components R1 and R2. FACET by Lab-Volt 17

5 3. To change the value of the positive power source in the OHM S LAW circuit block from 2.0 Vdc to 8.47 Vdc, the a. positive variable COURSE control is used. b. positive variable COURSE and FINE controls are used. c. positive variable FINE control is used. d. positive source is variable only to 6.0 Vdc. 4. A circuit board is inserted into the base unit when the a. base unit LEDs are on. b. ZIF connector is closed. c. ZIF connector knob is rotated CW with the power switch off. d. ZIF connector knob is rotated CCW. 5. The variable power sources in the OHM S LAW and BATTERIES circuit blocks read approximately 0V a. ZIF connector knob is in the CCW position. b. ZIF connector knob is in the CW position. c. positive supply controls are in the CCW position. d. negative supply controls are in the CCW position. 18 FACET by Lab-Volt