4-3
4
Digital I/O line.
The 4867's Relay Drivers are high-current open-collector drivers that are
designed to sink current to actuate relays, solenoids or other logic elements.
The driver chip Vcommon line must be connected to the external power
supply positive line to prevent damage to the driver IC. Place anti-back EMF
diodes across any inductive loads such as relay coils. Limit any inrush
current to 250 mA.
The 4867 contains a quad D/A converter with four output channels. The D/
A converter uses a 2.5 Vdc reference on the PC board to generate an accurate
0 to 5 Vdc output. Each D/A channel has a separate gain and offset
The 4867 contains a A/D converter with eight input channels. Each channel
has a programmable input range that can measure input voltages over
±
10,
±
5, +10 and +5 volt ranges. Channels 1 through 6 are used to measure the
six analog input signals. Channel 0 is used to measure the output of the
temperature converter. Channel 7 is used to measure the D/A reference
voltage as part of the 4867's selftest routine. The settings for Channels 0
affect how the temperatures inputs are measured. The settings on channels
1 through 6 affect how the individual channel measurement is made. Each
channel has individual gain and offsets which were set when the unit was
calibrated.
The 4867 contains a four channel multiplexer and thermocouple conversion
circuit that senses the output of type J thermocouples to measure temperature
over a -100
°
C to +400
°
C temperature range. The 4867 uses the multiplexer
to select the thermocouple to be measured. A reference thermocouple on the
PC board compensates for the temperature of the thermocouple conversion
IC. The thermocouple conversion IC electrically provides the ice bath
reference voltage, amplifies and linearizes the external thermocouple voltage
so it can be read by channel 0 of the A/D converter. The 4867 firmware
performs a four segment linearization correction on the channel 0 readings
using values saved when the unit was calibrated.
The Flash memory chip contains all of the 4867’s program instructions,
command tables, and power turn-on/self test routines. At power turn-on, the
4867 performs a self test on each functional block to determine whether
there is a gross system failure. Any self test error is displayed by blinking
a pattern on its LED(s).
