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Tektronix DM502
basic 3½ digit digital multimeter
Tektronix DM502

Produced from 1975 to 1980

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix DM502 is a basic 3½ digit digital multimeter plug-in for the TM500 system.

It was introduced in 1975 and superseded by the DM502A in 1980.

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).

Key Specifications

Voltage ranges 200 mV to 200 V in decade steps; 1 kV (DC) / 500 V (AC) top range
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

An "Option 2" instrument deletes the temperature measurement function,


Documents Referencing DM502

Document Class Title Authors Year Links
070-2088-01.pdf Book TM500 Series Rear Interface Data Book 1976


The DM502 circuit is built around a Siliconix LD110/111 DMM chipset.

The entire unit with exception of the temperature circuit can be elevated up to 1 kV above chassis ground. For this purpose, it is supplied through a mains-frequency isolation transformer with a 50 V primary that is supplied from the two 25 VAC windings in the mainframe connected in series. This transformer feeds a a discrete +5 V regulator, and an RC4194D regulator for +/–12 V.

The rear interface supports a digit-serial BCD output but the manual cautions that only the Temp Out, Temp GND and HI and LO inputs are factory-wired, the BCD connections must be soldered in by the user if needed – presumably because the digital section is not galvanically separated from the floating input ground. In Temperature mode, the floating ground is connected to the chassis ground (because the temperature circuit uses the mainframe's ±33 V supplies) but the V/A inputs are disconnected.



Some Parts Used in the DM502

Part Part Number(s) Class Description Used in
CA3046 156-0048-00 Monolithic integrated circuit transistor array 7104 7403N 7503 7B53A 7D12 DM502 S-52 Telequipment D34 7603 7613 7623 7633
Siliconix LD110/111A 156-0476-00 156-0476-00 156-1268-00 Monolithic integrated circuit 3½ digit A/D converter DM502 DM502A DM505