VOLTAGE REFERENCE INPUT
The ADC-4U15 allows for several different reference voltage configurations. The reference voltage determines the
voltage input range for all (4) analog input channels or (2) channels in differential mode. The following configurations
are selectable from the ADC-4U15 Setup. Option 1 is the default setting (this allows exactly 8 increments per mv).
Option 1: 4.096 volt - allows a (0 to 4.1) volt input range ((4) channel single ended) (= 0 to 4,096mv)
allows a (-4.1 to +4.1) volt input range ((2) channel fully differential) - 8 increments per mv
Option 2: 5 volt - allows a (0 to 5 volt)* input range or (-5 to +5) in differential mode (= 0 to 6,144mv)
(4) channel single ended or (2) channel fully differential - 5.3333 increments per mv
Option 3: 2.048 volt - allows a (0 to 2) volt input range or (-2 to +2) in differential mode (= 0 to 2,048mv)
(4) channel single ended or (2) channel fully differential - 16 increments per mv
Option 4: 1.024 volt - allows a (0 to 1) volt input range or (-1 to +1) volts in differential mode (= 0 to 1,024mv)
(4) channel single ended or (2) channel fully differential - 32 increments per mv
Option 5: .512 volt - allows a (0 to .5) volt input range or (-.5 to +.5) volts in differential mode (= 0 to 512mv)
(4) channel single ended or (2) channel fully differential - 64 increments per mv
Option 6: .256 volt - allows a (0 to .25) volt input range or (-.25 to +.25) volts in differential mode (= 0 to 256mv)
(4) channel single ended or (2) channel fully differential - 128 increments per mv
*the 0 to 5 volt option is based on a 0 to 6.144 volt range with only the 0 to 5 volt portion usable (see page 12).
SINGLE ENDED ANALOG VOLTAGE INPUTS
Voltages up to hundreds of volts may be divided down to the 5 volt range by using a simple resistance divider as
shown on the following page (the signal source must be capable of driving a 1 ma load). To determine the value
transmitted by the ADC for a specific voltage applied to the divider circuit use the following formula: (VI divided by
DF) times 51 = TV (where TV = transmitted value sent by the ADC, VI = voltage input to divider, DF = divider factor)
DF = full scale voltage divided by 5 volts. EXAMPLE: 100 volts full scale divided by 5 = 20 = DF. A 60 volt input to the
divider divided by 20 multiplied by 51 = 153 = TV, the value transmitted by the ADC (8 bit).
The voltage input source may be located up to several hundred feet from the ADC. The wire which connects the ADC
to the signal source should be a twisted pair to reduce possible input noise (22 or 24 gauge communication cable or
CAT5 typical). Shielded cable may be used to further protect against EMI or lightning noise (the shield should be left
disconnected at the source and connected to an earth ground/equipment ground at the ADC).
Lower millivolt signal levels (such as the output signals from a watt transducer, pressure transducer, load cell, etc.)
with typical full scale voltages of only 20 to 100 millivolts will require the addition of the VA-1, VA-2, VA-4 or VA-8
instrumentation amplifier. The VA-1 connects to any of the analog inputs and will convert a millivolt signal input to a 0
to 5 volt output for input into the ADC. Signal levels this low will may require shielded cable to reduce noise. An
adjustment on the VA-1 will set the input scale. The shield should be left disconnected at the source and grounded to
an earth ground at the VA-1. Applications requiring isolated analog inputs require the VI-8I linear opto isolated
amplifier.
NOTE:
When the analog inputs are left floating, (no connection) the ADC will transmit fluctuating numbers as a
result of noise present at the inputs. We recommend that any unused inputs be connected to GND (reference (-)) to
prevent possible errors on other channels (differential inputs should have both inputs shorted together).
FILTERING INPUT NOISE:
A .1 uf filter capacitor is installed on the ADC card (one for each channel) which
significantly reduces errors and fluctuation as a result of input noise. A 2.7 mf or 10 mf tantalum capacitor may added
for additional filtering (input response time will be slower).
Shown on the following pages in figures A, B & C are methods for reading contact closure, potentiometer movement
& light levels.
Page 8
INPUT SCALING AND OFFSETS
Analog inputs may be scaled and offsets added by opening the user interface and clicking Setup and then Analog
Setup. This allows you to directly display temperature, pressure, position, etc. by adjusting the raw analog data
coming from the sensor to the actual units (such as degrees, PSI, mm, GPM, RPM, etc,). The Precision setting allows
the units to be displayed in integer, tenth, hundreds, etc. Use the Suffix box to change the display from the default
Units to the required specifier. You may check the "Raw" checkbox to disable all formatting.
DIFFERENTIAL ANALOG INPUTS
The ADC-4U15 may be set to accept (2) fully differential inputs in place of the (4) single ended inputs. The differential
voltage input range is determined by the reference setting as shown on the previous page. The differential input signal
connects to terminals 1 and 2 for differential channel 1 and terminals 3 and 4 for differential channel 2. The GND
terminal connections are not used.
CONNECTION OF LOW LEVEL DIFFERENTIAL SIGNALS TO THE VA-1:
If low level differential inputs are
required, the VA-1 may be used to convert a differential signal into a 0 to 5 volt signal for connection to the ADC. The
VA series amplifiers have a reference input (for connection to the ADC reference) which is used to generate a 2.5 volt
offset (adjustable). The gain adjustment on the VA series amplifiers may be adjusted to allow for differential signals as
low as (+) and (-) 5 millivolts or as high as (+) and (-) 5 volts. Using the VA-1 will allow the use of all 4 single ended
inputs on the ADC-4U15 since the low level differential input to the VA-1 is converted to a single ended signal for
connection to the ADC-4U15.
Page 9
USB
1
2
3
4
Differential Analog Terminal
Block Connections
differential input #1 +
(Terminal 1)
differential input #1
-
(Terminal 2)
differential input #2 +
(Terminal 3)
differential input #2
-
(Terminal 4)
