Specifications

VOLTAGE INPUT AMPLIFICATION AND SIGNAL CONDITIONING
The ADC-16 defaults to a 0 to 5 volt input range (installation of a voltage reference will allow input ranges as low as 0 to
1.2 volts when using 8 bit inputs). When the input voltage range is required to be lower, (such as with a watt transducer
or load cell) an external instrumentation amplifier must be used to amplify the input signal to the 0 to 5 volt input range
of the ADC-16.
Several general purpose instrumentation amplifiers are available to amplify lower signal levels to the 0 to 5 volt range
required by the ADC-16 (for use with 8, 10 and 12 bit inputs). The VA-1 is a single channel amplifier for connection to
the ADC-4, ADC-8 or ADC-16. The VA-2, VA-4 and VA-8 amplifiers are two, four and eight channel versions of the
VA-1. The VA-1, VA-2, VA-4 and VA-8 all provide 15 turn potentiometer(s) for gain adjustment (amplification level). The
amplification level is adjusted for a 0 to 100 millivolt input at the factory. The amplification level may adjusted for signal
inputs as low as 0 to 5 millivolts or as high as 0 to 5 volts. Lower signal levels (such as the output signal 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 instrumentation amplifier. Signal levels this low will require shielded wire in place of a twisted pair.
The shield should be left disconnected at the source and grounded to an earth electrical ground at the VA-1.
CONNECTION OF DIFFERENTIAL SIGNALS: The ADC-16 inputs are single-ended. If 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-16. The VA
series amplifiers have a reference input (for connection to the ADC-16 reference) which is used to generate a 2.5 volt
offset. 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.
ANALOG LINEAR OPTOCOUPLERS: The VI-1I or VI-8I linear optocoupler instrumentation amplifiers may be used
when the analog input signal must be electrically isolated (such as with some types of pressure transducers, signals
with ground referenced offsets or for signals which must be isolated for safety).
VOLTAGE REFERENCE INPUT
Each 8 channel analog input port has a separate voltage reference input and each port may be selected to function in
any of the following three modes. NOTE: 10 bit inputs are limited to a 5 volt reference.
MODE (1).....Voltage reference equals power supply. With the factory jumpers installed, the reference (+) and
reference (-) will be equal to the power supply voltage (5 volts and ground, plus or minus .25 volts). The voltage input
scale will be 0 to 5 volts (20 millivolt resolution with 256 increments for 8 bit inputs or 5 millivolt resolution with 1,024
increments for 10 bit inputs). The ADC-16 will then transmit (255)* with a 5 volt input, (0) for a 0 volt input, (128) for a
2.5 volt input and other values corresponding to the following formula: voltage times (51) = X, where X = the integer
value transmitted. EXAMPLE: 1.9 volts times 51 = 96.9. The ADC-16 would then transmit (97) decimal (in binary) to
represent a 1.9 volt analog input. The use of the power supply for the voltage reference will be adequate for most
applications. MODE (1) is selected when both jumpers are installed (J1 and J2 for port #1, or J3 and J4 for port #2), all
8 channels of the analog port will then function in the MODE (1) configuration. *binary number represented in decimal
MODE (2).....Voltage reference equals calibrated external voltage reference equal to power supply voltage. This
method will provide a greater degree of accuracy for analog inputs which need to be referenced to the actual volt (use
of the power supply for actual volt reference may introduce small errors due to variations in the power supply caused by
activity of the ADC-16 functions). To select the MODE (2) configuration cut the (+) reference voltage jumper (J1 for port
#1 or J3 for port #2). The jumpers to the (-) reference voltage should be left in place (J2 for port #1 or J4 for port #2). A
calibrated voltage equal to the ADC-16 power supply (plus or minus .1 volt) should be applied to the voltage reference
input (terminal #9 (+) and #10 (-) on the RCT-8). The voltage input may be any well regulated power supply which can
be adjusted to the desired voltage without drift (for greater stability a temperature compensated power supply may be
used). To determine the proper voltage, measure the ADC-16 power supply voltage on the 28 pin 0809 chip (pins #11
and #13). The resolution will be equal to the reference voltage input divided by 256. All 8 channels of the analog input
port will then function in the MODE (2) configuration with J1 (port #1) or J3 (port #2) cut and the external voltage
reference connected. The ADC-16 has the capability of providing an on-board voltage reference by installing a
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317 adjustable voltage regulator, 500 ohm trimmer, 240 ohm and 390 ohm resistors on the top right side of the ADC-16.
MODE (3).....(8 bit only) Adjusted voltage reference input. In this mode of operation the voltage input level may be
adjusted to allow input of lower analog voltages (down to about 1.2 volts full scale). The MODE (3) configuration is
selected by removing the voltage reference jumpers (J1 and J2 for port #1 or J3 and J4 for port #2) and installing a
limiting resistor (3K typical) in place of both jumpers. It is important that both resistors be installed because the
reference voltage must be centered about the supply voltage of the 0809 chip. Conversion errors may occur (due to the
design of the 0809 chip) if the center of the reference voltage is not equal to the center of the supply voltage (plus or
minus .1 volt). The voltage reference device is then connected to the voltage reference input (terminal #9 (+) and #10 (-
) on the RCT-8). The voltage reference may be soldered directly to pins #12 (+) and #16 (-) on the 0809 chip for greater
stability. The voltage reference device may be a simple zener diode or LED for less critical applications (use (2) 180
ohm resisters in place of jumpers for LED). When the voltage reference is 2.5 volts or less, the installation of a 470 mf
capacitor on the ADC-16 is recommended (holes are provided near the center of the card above J3 with the positive
lead marked). The use of a temperature compensated voltage reference will result in greater accuracy and less drift.
You may contact our technical support staff for more information on the voltage references which we stock.
NOTE: The analog voltage input must not be higher than the ADC0809 power supply voltage for modes 1 and 2 or the
rated voltage of the voltage reference device for mode 3. In all cases the input voltage must not go negative (or
negative with respect to the reference in the case of MODE (3) operation). Failure to observe these voltage input
restrictions may result in erratic or incorrect conversion results on one or more of the analog channels.
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-16 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-16, 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-16.
The voltage input source may be located up to several hundred feet from the ADC-16. The RCT-8, RCT-16 or RCP-8
are used to make the wire connections. The wire which connects the RCT-8 to the signal source should be a twisted
pair to reduce possible input noise (22 or 24 gauge communication cable or CAT5typical). 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-16).
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-16. Signal levels this low will require shielded wire in place of the twisted pair. 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 optocoupler amplifier.
NOTE: When the analog inputs are left floating, (no connection) the ADC-16 will transmit fluctuating numbers as a
result of noise present at the inputs. We recommend that any unused inputs be connected to reference (-) to prevent
possible errors on other channels.
FILTERING INPUT NOISE: A .01 mf filter capacitor is installed on the ADC-16 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 page in figures A, B & C are methods for reading contact closure, potentiometer movement &
light levels.
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