HP 3478A Technical Manual page 24

3 3 4 78A 478A
Function and the "4 11" annunciator is on for the 4-Wire Function and the "4 11" annunciator is on for the 4-Wire
Ohms Function. The ohms reading can be displayed Ohms Function. The ohms reading can be displayed
either as a 5 1/2, 4 1/2, or 3 1/2 digit reading, dependent either as a 5 1/2, 4 1/2, or 3 1/2 digit reading, dependent
on the selected Number Of Digits Displayed (see on the selected Number Of Digits Displayed (see
paragraph 3-54). A .03 second or a .3 second delay is paragraph 3-54) . A .03 second or a .3 second delay is
also applied before each reading in the 3M ohm and 30M also applied before each reading in the 3M ohm and 30M
ohm Ranges, respectively. Refer to ohm Ranges, respectively. Refer to Table 1-1
1 for the Ohms Function's accuracy specifications. 1 for the Ohms Function's accuracy specifications.
The The 3478A 3478A will will
resistance if small negative voltages resistance if small negative voltages
exist on the circuit under test, or the exist on the circuit under test, or the
Ohms Sense and Input Leads are Ohms Sense and Input Leads are
reversed from each other. This only reversed from each other. This only
happens in the 4- Wire Ohms Function. happens in the 4- Wire Ohms Function.
3-30. 3-30. DC Current DC Current Measurements Measurements
3-31. 3-31. The The 3478A 3478A can can make
from 1uA to 3A in two ranges: 300mA and 3A. The from 1uA to 3A in two ranges: 300mA and 3A. The
ranges are protected from excessive currents and ranges are protected from excessive currents and
voltages by a 3A 250V fuse. Select the DC Current voltages by a 3A 250V fuse. Select the DC Current
Function to to measure Function measure dc cu dc currents
button. button.
3-32. 3-32. In the DC In th e DC Current Current Function, t
applied between the INPUT LO and A Terminals. Since a applied between the INPUT LO and A Terminals.
known value resistor (.1 ohm) is connected between the known value resistor (.1 ohm) is connected between the
terminals, a voltage proportional to the unknown cur- rent terminals, a voltage proportional to the unknown cur- rent
and the resistor is generated. This voltage is measured and the resistor is generated. This voltage is measured
by the 3478A's dc circuitry (Input Circuitry and A/D by the 3478A's dc circuitry (Input Circuitry and A/D
Converter). Converter).
3-33. 3-33. When When the the DC DC Current Current Function
right side of the display shows "MADC" or "ADC", right side of the display shows "MADC" or "ADC",
dependent on the range selected. The readings can be dependent on the range selected. The readings can be
displayed either as a 5½/2, 41/2, or 31/2 digit reading, displayed either as a 5½/2, 41/2, or 31/2 digit reading,
depending on the selected Number of Digits Displayed depending on the selected Number of Digits Displayed
(see paragraph 3-54 (see paragraph 3-54). Refer to ). Refer to Table 1-1
the DC Current Function's accuracy specifications. the DC Current Function's accuracy specifications.
Current inputs of greater than about I Current inputs of greater than about I
amp may cause the current shunt's (.1 amp may cause the current shunt's (.1
ohm Resistor) value to change slightly, ohm Resistor) value to change slightly,
due to self-heating. This may cause due to self-heating. This may cause
inaccuracies inaccuracies in in
Sufficient time should be allowed for the Sufficient time should be allowed for the
circuitry to settle after the measurement circuitry to settle after the measurement
is complete and before other critical is complete and before other critical
current measurements are made. current measurements are made.
3-34. 3-34. AC Current AC Current Measurements Measurements
3-35. 3-35. The 3478A The 3478A can can make
from 1uA to 3A in two ranges: 300mA and 3A. The from 1uA to 3A in two ranges: 300mA and 3A. The fre
Table 1-1 or or Table 4-
NOTE NOTE
show show a a negative negative
make dc dc current current measurements measurements
rrents by by pressing pressing the the
Function, the current he current is is
Function is is selected, selected, the
Table 1-1 or or Table 4-1 Table 4-1 for
NOTE NOTE
the the measurement. measurement.
make ac ac current current measurements measurements
quency response is from 20Hz to 20KHz. The ranges are quency response is from 20Hz to 20KHz. The ranges
protected from excessive currents and voltage by a 3A protected from excessive currents and voltage by a 3A
fuse. Select the AC Current Function to measure ac fuse. Select the AC Current Function to measure ac
currents by pressing the currents by pressing the
3-36. . 3-36
Table 4-
Current Function (see Current Function (see paragraph 3-30)
across a resistor is measured. The difference is that the across a resistor is measured. The difference is that the
resultant ac voltage is changed from ac to dc using the resultant ac voltage is changed from ac to dc using the
AC to DC Converter. Similar to the AC Volts Function, all AC to DC Converter. Similar to the
ranging is done in the converter. ranging is done in the converter.
3-37. 3-37.
right side of the display shows "MAAC" or "AAC", right side of the display shows "MAAC" or "AAC",
dependent on the range selected. The readings can be dependent on the range selected. The readings can be
displayed either as a 5 1/2, 4 1/2, or 3 1/2 digit reading, displayed either as a 5 1/2, 4 1/2, or 3 1/2 digit reading,
dependent on the selected Number Of Digits Displayed dependent on the selected Number Of Digits Displayed
(see (see paragraph 3-54 paragraph 3-54). Refer to Table 1-I or
the AC Current Function's accuracy specifications. the AC Current Function's accuracy specifications.
3-38. 3-38.
3-39. 3-39.
= = A A Autorange. Manual ranging is selected by pressing the Autorange. Manual ranging is selected by pressing the
AUTO/MAN button (if the 3478A is in Autorange) or by AUTO/MAN button (if the 3478A is in Autorange) or by
pressing either the pressing either the
annunciator on the display then turns on. The following annunciator on the display then turns on. The following
Since a
explains the different range modes. explains the different range modes.
3-40. 3-40.
higher range each time the higher range each time the
highest selectable range depends on the function highest selectable range depends on the function
selected (e.g. 300V for the AC Volts and DC Volts selected (e.g. 300V for the AC Volts and DC Volts
Functions). If a function is selected with its highest range Functions). If a function is selected with its highest range
the
lower than the previous range, the multimeter defaults to lower than the previous range, the multimeter defaults to
the new highest range. the new highest range.
3-41. 3-41.
lower range each time the lower range each time the
for
lowest selectable range depends on the function lowest selectable range depends on the function
selected (e.g. 30mV for the DC Volts Function). If a selected (e.g. 30mV for the DC Volts Function). If a
function is selected with its lowest range higher than the function is selected with its lowest range higher than the
previous function, the multimeter defaults to the new previous function, the multimeter defaults to the new
lowest range. lowest range.
3-42. 3-42.
range when this mode is selected. The mode is selected range when this mode is selected. The mode is selected
when the 3478A is first turned on or by pressing the when the 3478A is first turned on or by pressing the
AUTO/MAN button (if in Manual Range). If Autorange is AUTO/MAN button (if in Manual Range). If Autorange is
enabled, the 3478A upranges when the reading is at or enabled, the 3478A upranges when the reading is at or
above ± 303099 and downranges at or below +027000 above ± 303099 and downranges at or below +027000
(delete one or two zeroes from the numbers for the 4 1/2 (delete one or two zeroes from the numbers
and 3 1/2 Digit modes, respectively). The numeric range and 3 1/2 Digit modes, respectively). The numeric range
points are irrespective of decimal placement. Refer to points are irrespective of decimal placement. Refer to
Figure 3-5 for the autorange points (the example is for Figure 3-5
the DCV Function; other functions are similar). the DCV Function; other functions are
fre
3-43. 3-43.
3-44. 3-44.
Internal, Single, and External. In addition to these, a Hold Internal, Single, and External. In addition to these, a Hold
3-5 3-5
A button. A button.
∼ ∼
The The AC AC Current Current Function Function is is similar
paragraph 3-30); a voltage drop
When the e AC When th AC Current Current Function Function is is selected,
). Refer to Table 1-I or Table 4-1
Ranging Ranging
The 3478A The 3478A has has two two range range modes:
   
or or buttons. The "M RNG" buttons. The "M RNG"
Uprange Uprange. The 3478A upranges to the next . The 3478A upranges to the next
 
Downrange Downrange. The 3478A downranges to the next . The 3478A downranges to the next
 
button is pressed. The button is pressed. The
Autorange. The 3478A selects the optimum Autorange. The 3478A selects the optimum
for the autorange points (the example is for
Triggering Triggering
The 3478A has th The 3478A has three local ree local trigger mode
TM 11-6625-3071-1 TM 11-6625-3071-14 4
are
similar to to the the DC DC
; a voltage drop
AC Volts Function, all
selected, the the
Table 4-1 for for
modes: Manual Manual and and
button is pressed. The button is pressed. The
for the 4 1/2
similar).
trigger modes: s: