Keithley dual multiplexer plug in card 37xx series keithley 3720 the keithley 3720 is a dual 1x30 multiplexer plug in card that offers two independent banks of 1x30 two pole multiplexers it is ideal for general purpose switching including temperature measurements the two banks can automatically be connected to the series 3700a mainframe backplane and optional dmm through the analogue backplane connection relays this connection allows the mainframe to reconfigure the card to a single 1x 6