LOW THERMAL DESIGN
Measurements International's Model 4220A utilises ultra-sensitive high efficiency polarized relay technology to deliver an automated low thermal matrix scanner. The relays used are 2 coil latching type, requiring only a short millisecond pulse to activate to eliminate self heating in the relay. The relay boards are thermally isolated to maintain thermal equilibrium in the switching area.

The Model 4220A has a total of 80 inputs and 8 outputs. For resistor applications it will handle up to 20 four terminal resistors and 40 two terminal connections for voltage applications. Connections to the resistors and measuring apparatus are made at the back of the scanner. Provisions have also been made for connecting the shields of the resistors.

True four terminal Matrix Scanner
20-four terminal inputs
40-two terminal inputs
Front panel or bus operation
Thermals in the nanovolt region

OPERATION
The Model 4220A provides an easy means for intercomparing resistors, standard cells or 10 volt references. The relays selecting the rear panel input terminals are activated by front panel push-buttons or by commands sent over the IEEE-488 interface bus. The rear panel inputs are selected by pressing the channel desired and then the A or B button. The corresponding LED will be illuminated.

Several protection circuits are built into the 4220A. The corresponding LED is driven directly from a separate contact on the relay. Only one set of relays can be activated at any one time. It is necessary to open the closed set before another can be activated on the same side.

APPLICATIONS
Thermometry scanner
Resistance calibrations
Low thermal voltage measurement