RST Flexi-Mux Instruction Manual
ELM0029B
RST Instruments Ltd.
Page 7
the common terminals (A, B, C, D) are electrically disconnected from all the sensor input
channels. Reset should always connect to a datalogger control port. When programming,
a delay (
≥100ms) after setting Reset high must be included or the Flexi-Mux will not clock
between ports.
5.1.2
Clock
Pulsing the Flexi-
Mux “clock” line high (with “reset” set high) advances the channel.
Whether the Flexi-Mux advances 2 positions or 4 positions depends on the internal DIP
switch settings (Section 5.2). When the reset first goes high, the common terminals A, B,
C and D are disconnected from all sensor input terminals. With the Flexi-Mux set in the 4-
Pole mode, when the first clock pulse arrives the common terminals are switched to
connect with the sensor input channel 1 (consists of 5 wires: A, B, C, D and shield). When
a second clock pulse arrives, the common lines are switched to connect to channel 2.
The multiplexer advances along the leading edge of the positive-going clock pulse. The
voltage level must fall below 1.5VDC and then rise about 2.0VDC to clock the multiplexer.
The clock pulse should be at least 1 ms long. A delay (typically 10 to 20 ms) is inserted
into the datalogger program between the beginning of the clock pulse and the
measurement instruction to ensure sufficient settling time for the relay contacts.
In general, a control port is used to clock the multiplexer. However, switched excitation for
the sensors can also be used (as stated in Section 5.1). See Section 5.3 for more details
on datalogger connections with the Flexi-Mux.
If several multiplexers are required, the Flexi-Mux allows a virtually unlimited number of
units (limited by cable losses) to be connected in series because the Flexi-Mux boosts the
clock and reset signals through its circuitry. Thus, no control voltage is lost through the
ports. An adequate 12VDC power source must be maintained through each multiplexer
for this to function correctly.
5.1.3
Ground
The Flexi-
Mux “ground” terminal is connected to the datalogger power ground.
5.2
DIP
S
WITCH
S
ETTINGS
Internal DIP switches on the Flexi-Mux control whether it switches 2 or 4 wires each time it
is clocked. To change the DIP switch settings, remove the dust cover located on the base
of the unit. The piano-key style DIP switches are accessed through this hole as shown in
Figure 5-2. Adjust the DIP switches as outlined below. There is also a diagram on the
Flexi-Mux itself which reflects these settings (item 6, Figure 4-1).