Teledyne 6400A Instruction Manual page 161

TAI Model 6400A SO
These 3 outputs are controlled by a common pot (R34) on the upper edge of the card.
If the temperature readouts are in error:
1. Adjust R34 of the Status/Temp board to read 2.577 VDC between test point 6 and test point
2. This will cause all of the readouts to accurately measure their respective temperatures.
9.3.4.2 Display Brownout
During low AC line conditions the display can lock up due to insufficient voltage. When low
line conditions are approaching, this circuit senses the condition by monitoring the un-regulated
+5VDC in the Power Supply Module. If brownout conditions are met, the DISP_BROWNOUT
line is asserted and the CPU sends a hardware RESET command to the display and sends a
BRNOUT RESET pulse back to U4. Brownout conditions will be noticed by the display flashing
every 8 seconds.
9.3.4.3 Status Output Lines, External Contact Closures
The Status lines consist of 2 active input lines, and 12 active output lines. Additional circuits are
present on the board but currently unused. Individual lines are set or cleared under CPU control
depending on the assigned alarm condition. The CPU also monitors the 2 input lines for remote
calibration commands. The status inputs and outputs are terminated at the rear panel, see
schematic diagram 01114.
The output lines are opto-coupled NPN transistors which can pass 50 ma max of direct current
with a voltage of 30 VDC max (see Schematic 01087).
The input lines are optically coupled with inputs pulled up to +5VDC. External contacts can be
contact closures or open channel transistor contacts. DO NOT apply any voltage, since +5VDC
is supplied internally (refer to Figure 2-2 and Schematic 01087 for details).
Individual status lines can be set or cleared using the DIAGNOSTIC mode SIGNAL I/O. This
can be useful for simulating fault conditions in the analyzer to see if external circuitry is working
correctly. See Table 6-3 for pin assignments.
9.3.4.4 Isolated 4-20 mA Current Output
4-20 mA current loop option replaces the voltage output of the instrument with an isolated 4-20
mA current output. The current outputs come out on the same terminals that were used for
voltage outputs (see Figure 2-2). It is programmable for 4-20mA or 0-20mA and has a 1500 V
common mode voltage isolation and 240 V RMS normal mode voltage protection. V
max which is sufficient to drive up to a 1000 ohm load. Verify that the jumpers on the
motherboard are set properly for the current output mode (refer schematic 01471 and 01248).
See Section 9.3.3.1 for the 4 - 20 mA current output calibration procedure.
There are two methods to measure the output of 4-20mA option.
Analyzer Operator Manual, 02164, Rev. G
2
9-43
= 28V
loop