CDM 250 Digital Multimeter User

CDM 250 Digital Multimeter User Instructions

Getting Started

The Tektronix CDM250 Digital Multimeter measures analog quantities and displays them in digital form. This multimeter takes the following measurements:

Measurements aned Ranges

ð Direct and alternating current from 200mA to 10 A in six ranges

200 mA

2 mA

20 mA

200 mA

2000 m A

10A

ð AC and DC voltage from 200 mV to 500 V in five ranges

200 mV

2 V

20 V

200 V

500 V

ð Resistance from 200 W to 20 MW in six ranges

200 W,

2 KW

20 KW

200 kW

2000 KW

20 MW

Commonly used symbols

Prefix	Symbol	Power of 10
tera	T	10¹²
giga	G	10⁹
mega	M	10⁶
kilo	K	10³
milli	m	10^-3
micro	µ	10^-6
nano	n	10^-9
pico	p	10^-12

All values are displayed on a 31/2 digit, light-emitting diode (LED) indicator. Alternating voltages and currents are displayed in RMS values.

The CDM250 has a locking, multiposition handle that folds under the instrument to allow stacking with other instruments of the same series. It is delivered with a set of test leads, a 115 V power cord, an installed line fuse for 115 V operation, and this manual.

Preparing the Digital Multimeter for Use - Back Panel

Check the following items prior to operating the CDM250 Digital Multimeter for the first time (Refer to the following figure for the locations of items):

Line Voltage Selectors, Power Input, and Fuse Locations

I will check this before you begin - do not change the settings

CAUTION. To prevent damage to the instrument, set the line voltage selectors to the proper voltage setting and install the correct line voltage fuse before operating the equipment.

1. Set the line voltage selectors to the input line voltage. These selectors connect internal wiring for various line voltages. This product is intended to operate from a power source that does not supply more than 250 VRMS between the supply conductors or between either supply conductor and ground. For line voltage ranges, refer to Appendix A: Specifications on page 11.

WARNING. To prevent electrical shock, unplug the power cord and disconnect the test leads from any voltage source before checking or replacing the fuses. Students will not work with fuses in this class.

2. Check that the correct line fuse is installed. The line fuse provides protection if the equipment malfunctions or an overload occurs.

3. Check that the correct function fuse is installed. The function

fuse provides protection when using the 2 A input jacks.

WARNING. To prevent electrical shock, connect the power cord to a properly grounded power source. The outside (ground) of this connector is connected through the equipment to the power source ground. Do not remove the ground lug from the power cord for any reason.

4. Connect the input power cord. Use only power cords that are equipped with a third conductor that provide a safety ground connection. Use only the power cords specified for this equipment.

Front Panel

The following figure shows the front-panel controls, connectors, and indicators with brief descriptions of the items following the figure.

1. POWER button.

Powers the CDM250 on or off.

Out is off

Push in for On. Power ON is indicated by the LED display.

2. 10 A UNFUSED jack. Input connector for positive (red) test lead when instrument is used to measure high current (over 2 A but less than 10 A).

3. V–_. Input connector for positive (red) test lead. Used for AC volts, DC volts, and ohms (_) functions.

4. LED Display. Shows voltage, current, or resistance value. Display shows the number 1 at the extreme left in an over range condition. Negative voltages or currents are indicated utomatically with a minus (–) sign at the extreme left of the display.

5. RANGE buttons. Push to select the highest value of the voltage, current, or resistance to be measured.

6. FUNCTION buttons. Push in only one button to select VOLTS (voltage), A (current), or

W (resistance). Only one function will work at a time.

7. AC/DC button. Push in to measure alternating current or AC voltage; reset to the out position for direct current or DC voltage. The AC/DC button may be in either position when the meter is used for checking resistance.

8. COM jack. Input connector for common (black) test lead. Used for AC or DC volts, ohms, and current functions. This connector is not connected to the power source ground through the instrument.

9. 2 A jack. Input connector for positive (red) test lead when instrument is used to measure current values up to 2 A.

Taking Measurements

This section of the manual explains how to take the following measurements:

ð AC or DC voltage

ð AC or DC current

ð Resistance

It also explains how use the CDM250 Digital Multimeter to check diodes.

Preparations for Measurement

1. Be sure that the CDM250 Digital Multimeter is connected to a specified power source and that the LINE VOLTAGE SELECTORs are set to the proper position. Refer to previous discussion Preparing the Digital Multimeter for Use.

2. Check that the FUNCTION and RANGE buttons are in the correct position. If the value to be measured is unknown, start at the highest range.

3. Be sure the red test lead is in the proper input jack for the measurement to be made.

Measuring AC or DC Voltage

1. Connect the black test lead to the black COM jack.

2. Connect the red test lead to the red V jack.

3. For DC voltage, set the AC/DC function button to the out position. For AC voltage set the AC/DC function switch to the in position.

4. Push the VOLTS function button in to lock it.

5. Determine the highest anticipated voltage, and push in the corresponding range button. When the voltage is unknown, select the highest range.

6. Push the POWER button to the ON position. NOTE. Voltage readings are taken in parallel with the component or device being measured.

7. Connect the test leads, and read the displayed value.

NOTE. Remove the red test lead from the circuit or component being tested before changing ranges.

Measuring AC or DC Current

1. Connect the black test lead to the black COM jack.

2. For current up to 2 A, connect the red test lead to the white 2A jack. For current between 2 A and 10 A, connect the red test lead to the white 10A UNFUSED jack.

CAUTION. The 10 A UNFUSED jack is not protected. Excess current may damage the instrument.

3. To measure alternating current (AC), set the AC/DC button to the in position. To measure direct current (DC), set the AC/DC button to the out position.

4. Push the A (amperes) button in.

5. Determine the highest anticipated current, and push in the corresponding range button. When the current value is unknown, start at the highest range.

NOTE. Current readings are taken in series with the component or device being measured.

6. Push the POWER button to the ON position.

7. Connect the test leads, and read the display value.

NOTE. Remove the red test lead from the circuit or component being tested before changing ranges.

Measuring Resistance

1. Connect the black test lead to the black COM jack.

2. Connect the red test lead to the red V jack.

3. Push the W (ohms) function button.

4. Determine the highest anticipated resistance on the range scale, and press the corresponding range button.

CAUTION. To prevent damage to the equipment, turn off all power to the circuit or component being measured.

5. Push the POWER button to the ON position.

6. Connect the test leads, and read the display value.

NOTE. When the component being tested is in a circuit where parallel current paths offer low resistance, the above test may require disconnecting one end of the component from the circuit.

Checking Diodes

1. Connect the black test lead to the black COM jack.

2. Connect the red test lead to the red V-_ jack.

3. Push in the _ (ohms) function button.

4. Simultaneously push the 200 and the 2K range buttons to the in position.

CAUTION. To prevent damage to the equipment, turn off all power to the circuit or component being measured.

5. Connect the red test lead to the anode and the black test lead to the cathode of the diode.

6. Push the POWER button to the ON position. A reading of about 25.0 to 90.0 should appear on the display.

Multiply the result by 10 to arrive at the forward voltage drop in mill volts.

If the reading on the display is 1 (over range indicator), the diode may be defective (open).

If the reading is 00.0, the diode is defective (shorted).

7. Connect the black test lead to the anode and the red test lead to the cathode of the diode. A reading of 1 (over range indicator) should appear on the display. If any other value is displayed, the diode is defective. On some diodes the meter might flash a high number for a very short period of time, but the reading should go to the over range indicator.

NOTE. When the diode being tested is in a circuit where parallel current paths offer low resistance, the above tests may require disconnecting one end of the component from the circuit.