HP 740B Operating And Service Manual page 17

Section ill Model 740B
j. Set VOLTAGE SET control for first five
digits of desired output voltage as indicated
by the digital readout tubes. Set STANDARD
VERNIER control for sixth digit of output
voltage as indicated by the meter.
- - - - N O T E - - - -
Each integer of the sixth digit
is represented by one major
division on the meter.
k. Set CURRENT LIMIT control to desired maxi-
mum limit of output current. (See Paragraph
3 -38 for a detailed discussion on using the
CURRENT LIMIT control. )
1.
Depress OUTPUT pushbutton. OUTPUT indi-
cator glows to indicate application of output
voltage to load.
m. To remove output voltage, depress OUTPUT
pushbutton. Indicator light goes out to indi-
cate removal of output voltage from OUTPUT
terminals.
I.-----WA-R-N-I N-G
---"1
ALWAYS DE -ENERGIZE OUTPUT
ORSETVOLTAGESETANDSTAN-
DARD VERNIER CONTROLS TO
ZERO WHEN MAKING CHANGES
IN THE OUTPUT TERMINAL CON -
NECTIONS.
Figure 3 -4. Local Sensing
3-16. SENSING.
3-21. REMOTE SENSING.
3 -22. Remote sensing should be used whenever the
740B is delivering current to a load and whenever the
load is away from the output terminal box.
3 -23. Remote sensing is accomplished by connecting
the + and - SENSE terminals to the load using ex-
tension leads. The + SENSE terminal must be con-
nected to the + end of the load and the - SENSE ter-
minal must be connected to the - end of the load
(Figure 3 -5).
LOAD
+
+SENSE
-OUTPUT
- SENSE
+OUTPUT
Figure 3 -5. Remote Sensing
OUTPUT CA8LE
hp
110558
740B-RO
3-18. LOCAL SENSING.
3 -19. Local sensing can be used whenever the operating
conditions require little or no current from the 740B
output or when the load is connected directly (through
very short leads) to the output box terminals.
3 -20. Local sensing is accomplished by connecting
the + SENSE terminal to the + OUTPUT terminal and
connecting the - SENSE terminal to the - OUTPUT
terminal (Figure 3 -4). The connections should be
made with short conductors, preferable solid copper
wire.
3-17. The purpose of the SENSE terminals is to fur-
nish voltage feedback from the load to the main loop
amplifier. If current is being drawn from the OUTPUT
terminals, small voltage drops occur in the output
leads since they are not perfect conductors. This
results in slightly low voltage at the load. If the
SENSE leads are connected to the load, this low volt-
age condition is "sensed" by the main loop amplifier.
The amplifier then increases its output voltage to com-
pensate for the voltage drop in the output leads.
Voltage drop in the SENSE leads is insignificant, since
very little current flows in these leads.
3-6 01794-1