Operator`s manual

1.3 Description
The SMX4030/32 are 35 channel models that can be arranged in up to four groups of 8:1 differential channels. The
SMX4032 is a high reliability instrumentation quality scanner specifically designed for switching in applications
requiring precision low noise and low leakage. The most outstanding feature of this model is a very low Thermal
EMF, resulting is highly accurate Ohms, low Voltage, temperature and other sensitive applications requiring low
high precision and low noise. For cost sensitive applications, where these issues are not as critical, the SMX4030
offers an economical solution. Though inferior to the SMX4032, the non isolated SMX4030 is a much better
switching card compared to similar plug-in products on the market.
When using an SMX2040 series 6-1/2 digit PXI DMMs, or similarly accurate DMM, it is necessary to use the
Instrumentation quality SMX4032 scanners in order to maintain full measurement accuracy provided by the DMM.
These scanners are software configurable on the fly, and can handle several pre-defined switching configurations,
such as TwoWire, FourWire, SixWire, Universal, TwoGroups, FourGroups,ColdJunction and Disabled. In the
TwoWire configuration, the scanner is a 35 channel multiplexer. In the FourWire configuration, it automatically
selects two simultaneous channels, allowing a DMM or other device to connect to four individual lines. In the
SixWire configuration six wires, or three differential channels are selected simultaneously, providing such
applications as six wire guarded in-circuit measurements (see SMX2044, SMX2064 DMMs for details). The
Universal configuration turns the scanner into a pseudo matrix structure, allowing any relay, including channel
relays, tree relays and configuration relays, to be closed or open, including multiple relays. The TwoGroups and
FourGroups configurations split the Scanner into several independent Two-Wire multiplexers. When in the
ColdJunction configuration, the Dbus is connected to the Abus while all other channels are open, to facilitate the
measurement of the Cold Junction temperature sensor of the SMX40T module, or a user cold junction sensor.
Figure 1-1. Simplified diagram of the SM4030 relay scanners.
In the TwoWire, FourWire, SixWire, TwoGroups, and FourGroups configuration, the switching sequence includes
the opening of previously selected channels and then closing of the selected channel(s) relay. In the case where
multiple channels are supposed to be closed, such as in FourWire configuration, these channels are closed
simultaneously so that no additional time beyond the actuation time is consumed. Break-before-make operation is
maintained due to an active high speed turns off circuit, which shuts off the energized coil’s current very quickly as
compared to the turn on time.
Signametrics 6