The Tektronix DM502 is a basic 3½ digit digital multimeter plug-in for the TM500 system.
It has an Int/Ext switch that allows alternate input connections via the rear interface to be selected.
The DM502 is available with an input for temperature measurement with a transistor temperature probe (P6430) using an NPN transistor, e.g. a 2N2484 (any NPN-Transistor with hFE >150 can be used).
The DM502A model adds an input for a PT-100 temperature probe (P6601), a True RMS converter, and offset circuits to read dB directly in all ranges. An "Option 2" instrument deletes the temperature measurement function, P6601 temperature probe, and all internal circuits associated with this function. The rear interface of DM502A is limited compared to the DM502: No current input and no reading output, see gallery below.
The 2 kΩ measurement range (+HI in DM502A) can be used for diode testing, since a current source of 1 mA is active and the reading corresponds to the (forward) voltage drop of the diode in Volts. The voltage can rise to a maximum of 10 V. A second voltmeter is needed to measure the voltage if 2 V are exceeded.
|Voltage ranges||200 mV to 200 V in decade steps; 1 kV (DC) / 500 V (AC) top range|
|Input impedance DM502||10 MΩ or direct JFET input >2 GΩ (by internal jumper)|
|Input impedance DM502A||10 MΩ|
|Current ranges||200 μA to 2 A in decade steps|
|Resistance ranges||200 Ω to 20 MΩ in decade steps|
- Tektronix DM502 Multimeter Repair by NFM @ YouTube