Tektronix Keithley AIM4 Isolated High-Level Analog Input Module Rev. B User manual
AIM4
Isolated High-Level Analog Input Module
The AIM4 Isolated High-Level Analog Input Module provides isolation and signal conditioning for four channels of voltage input (from *5OMV to *5V) or current loop input. Because the input channels are completely isolated from other channels and from
the system ground, the AIM4 module accepts signals with common mode voltages as
high as *50W, and provides protection to #JOV (normal mode). Channel-to-channel
isolation is 500V.
The AIM4 module provides switch selected gains of xl or x100. By changing resistor
and potentiometer values, individual local gains can be selected for each channel.
The AIM4 module may be placed in slots 3-10 of the baseboard (slots 2-10 if AMMl is
used). To install the module, remove the top cover and insert the module in the desired
slot with the component side facing the power supply. Place the AlM4 module as far
away from the power supply as possible to minimize noise and thermal effects.
CAUTION: Always turn off the power before installing or removeing modules. To
minimize the possibility of EM1 radiation, never operate the system with top
removed. Connect the + and -
inputs of unused channels together.
cover
User-Configured Components
Gain amplification for each channel can be changed by setting switches SW.-S104 to the
desired positions (xl or x100). As shipped the AIM4 is configured for xl gain (see
Figure 1).
Installing resistors in the appropriate locations provides current to voltage conversion,
allowing connection of current loop inputs.
All inputs are connected to a bank of screw terminals, which provides positive and
negative (high and low) terminals for each of the four input channels. See Table 1 for
summary of user-configured components.
Table 1. User-Configured Components on the AIM4
Name Designation Function
Switches lOl-104 SlOl, Sl.02, SlO3, S104 Gain setting channel 0, 1, 2, 3 (xl or x100)
Potentiometer Rlffl, R105, RlO9, Rll3 Trim gain for each channel
Resistors User Installed
Screw Terminals 162
Optional current voltage resistors.
Innut saew terminals. channels O-3
Document Number: 500-91401 Rev. B
AM41
AIM42
Figure 1. AIM4 Module Configuration
Connections
Terminals for connections to the AIM4 module are marked on the module. Typical con-
nections are shown in Figure 2. The use of shielded cable is recommended to minimize
noise pick up and the possibility of EMI radiation. One end of the shield should be
connected to the AIM4 ground and the other end left disconnected. The shield should
not be used as a signal path.
WARNING: Dangerous user-supplied voltages may be present on the input terminals.
CAUTION: Maximum input with xl gain is f5V. Maximum input with xl00 gain is
*5OmV.
SHIELD
Figure 2. Typical AIM4 Connections
Gain Adjustment
Switches SlOl-S104 set the gain applied to channels O-3 to either xl or x100. To set the
gain, place the switch in the desired position. Note that the module is configured for
xl gain as shipped. Remember that the maximum input voltage is i5V (xl gain) or
st5OmV (x100 gain). The maximum signal output range of the AIM4 module is k5V. Do
not apply gains when the resulting voltage will exceed &5V or measurement errors will
result.
By changing the values of user-installed resistors, alternate gain factors can be applied
to signals connected to the AIM4 module. In this way, the gain for each channel can be
determined.
The selection of a resistor should be based on the following formula:
G =1 + 10,000/R
Where G is the gain applied to the signal and R is the value in ohms of the installed
resistor.
Gain Trimming
Potentiometers RlOl, RI.05, R109 and Rll3 are provided for trimming the gain resistors
R102, R106, RllO and Rl14. If new gain resistors are reinstalled, different potentiometers
may be required.
AIM43
The relationship of the potentiometers and the gain resistor on the total resistance is
described by the formula:
Where RT is the total resistance (the value which ultimately affects the gain factor), R,
is the value in ohms of the gain resistor, and RP is the value in ohms of the potentiometer (trimmed to the desired value).
Current Inputs
With the installation of optional resistors in user-installed locations, the AIM4 module
can be configured to accept floating current loop inputs. The resistors are installed between the high and low input terminals converting the current range of the signal to an
appropriate voltage range.
The selection of the resistor is based on Ohms law:
E=I.R
Voltage (volts) = Current (amps) * Resistance (ohms)
Because the AIM4 module has an input range of *5V (with xl gain), these resistors
must convert the expected current range into a voltage range within these limits.
Therefore, volts should be set to 5, and current set to the upper limit of the expected
current range.
With a signal expected to range from 4 to 2OmA, for example, Ohm’s law yields the
following equation:
5 (volts) =
.02 (amps) * R (resistance)
R =250
As a result, a 25O!J resistor should be instaIled for that signal range. The resulting
voltage range of 1 to 5V can be further amplified by the PGA (on the AlMl module) if
the input range of the A/D converter is set to *lOV, or 0-1OV.
If there are several loads on the loop (if, for example, an analog chart recorder is being
driven at the same time), the compliance voltage at the current loop transmitter may be
exceeded. If this is the case, a smaller resistor (possibly 25Q) can be installed, and more
gain applied to the signal, either globally at the PGA, or locally by changing resistors.
Arm-4
Additional loads in series with the current loop can be connected on either side of the
isolated input.