The
3B Series Subsystem
Q. Is the 4-to-20 mA output of the 3B39 isolated from loop
power?
A. Yes. The current output is isolated from the input and from the
loop power.
Q. On the 3B system, can I power the current outputs without
24 V DC power?
A. Yes. A 0 to 400 W load, per module, can be driven by using the
+15 V power supply voltage provided from models AC1300 or AC1301 AC/DC
supplies, within the power supply current output rating. This is obtained
by strapping pins 1 and 4 on the backplane P3 connector.
Q. Are the outputs from a 3B37 thermocouple module linearized?
A. No. A common practice is to use a polynomial statement via software
in the user's system. The transfer function of the 3B37 is shown in
the 3B Series Users Manual. A 3B47 thermocouple module does provide
a linearized output.
Q. How can I isolate an input signal and also isolate the
output from the power supply ground?
A. Use an output module in conjunction with an input module, i.e.,
a 3B31 and a 3B39. The output of the 3B31 is the input to the 3B39.
(This is arrangement will provide 3-port isolation.)
Q. I have a 3B16 strain gage module, but I need bandwidth
of 1 kHz. Can I cut out the filter inside the module?
A. No. It's not that simple. What you need is a 3B18 module!
Q. How do I set up the a 4-20 mA output from a 3B Series module
to map with either the - 10 V to +10 V or 0 to + 10 V output signal?
A. All modules are shipped to provide a 4-20 mA current output corresponding
to a 0 to + 10 V voltage output. This current output range can be quickly
changed to correspond to a - 10 V to + 10 V output by selection of
a supplied jumper on the bottom of the module. A jumper also exists
to change the output current range to 0-20 mA.
Q. When I plug my configurable "3BXX-00" module
into the backplane, I get - 10 volts out. What should I do?
A. Plug the configured AC1310 ranging card onto the module first.
Until the AC1310 module is inserted, the 3BXX-00 module is not configured
for any gain.
Q. On our 3B RTD modules, how does Analog Devices provide
linearization. Do you use two end points?
A. No. The linearized RTD modules use three points to determine linearization
for each input temperature range: TMIN, TMID, TMAX.
Q. I'm using a 3B39 isolated output module. When I apply a
0 to + 10 V input signal to the screw terminals just above the module
on the backplane, I can't get 4-20 mA output signal?
A. The 3B39 voltage input signal (0 to + 10 V or -10 V to +10 V) is
to applied to the 3B39 through either the P1 or P2 system 26-pin connector
on the backplane. The isolated output current appears on the screw
terminals.
Q. I have a 3B18 strain gage module. My bridge is imbalanced
at the "zero" point. How do I zero suppress? It's not in
the manual.
A. There is no zero suppression available on the 3B18. However, model
3B16 does provide zero suppression.
Q. Do you have an isolated input strain gage module?
A. No. The output from the 3816 or 3B18 modules can be applied to
the input of an isolated module such as model 3B31, to provide an isolated
strain gage signal.
Q. Why can't the 3B16 strain gage module handle 100 W load
cells?
A. The 3BI6 provides +10 V of excitation with approximately 35 mA
load capability. A 100 W strain gage requiring +10 V excitation would
need 100 mA driving capability. To drive a 100 W bridge, use model
3B18 with a switch selected +3.3 V excitation.
Q. Do I have to return the current output from 3B modules
back to the same module screw terminal or can I use a common return
path for all my 3B current outputs?
A. With nonisolated 3B series modules you may use the loop power supply
return for all the modules. You will of course lose the overvoltage
protection that each module offers on its current return.
Q. How can I get a voltage output from my 3B39 or 5B39?
A. These output modules produce a 0 to 20 mA or 4 to 20 mA current
signal. These currents can be run on twisted pair wires for some distance
and then through a resistor. The current through the resistor develops
a voltage drop across it (see Ohm's law). If a 250 ohm resistor is
used, the voltage signal will be +1 to +5 V for a 4 to 20 mA current.
This voltage signal is not a true "voltage source" with a
very low impedance, and should be measured by a high input impedance
device for best accuracy.
Q. What power supply do I use with a 3B01 backplane fully
loaded with 3B16 or 3B18 modules?
A. A "fully loaded" 3B01 means 16 channels. Each 3B16 draws
45 mA from the +15 V supply and each 3B18 draws 50 mA from the +15
V supply. 16 3B16 modules would require 720 mA total, and 16 3B18 modules
requires 800 mA. The only power supply that can provide this is the
AC1307. It's +15 V supply provides 800 mA typical.
Q. What cable do I use with 3B/5B backplane when interfacing
to another manufacturer's board?
A. If the manufacturer is one of our partners who actively supports
the 3B and 5B series, they will have cables in their product line to
accomplish this. If you are using a board from another manufacturer
and they do not offer a cable, you can bring the 3B/5B input and output
signals to screw terminals with the combination of an AC1315 cable
and an AC1324 screw terminal panel. You will then be able to hard wire
to your data acquisition board or its termination panel.
Q. How can I adjust the bandwidth on 3B or 5B Series modules?
A. The only module that allows you to change the bandwidth is the
3B18 strain gage module. The directions for changing the bandwidth
using external components are in the user's manual. On all other 3B
and 5B Series modules, the bandwidths are fixed and cannot be changed.
The specification table for each module will give you its bandwidth.
Q. How can I obtain the custom-ranging program which will
help me determine whether or not Analog Devices can make 5B or 3B
custom modules for my particular input and output ranges?
A. Download the program from our web
site.
