|
 Being
a phase-sensitive carrier-demodulator instrument (rather than fully
DC), the single-channel Model 4078 is intended for applications
involving transformer coupling to the transducer bridge (as with rotary-transformer
torque sensors) and for applications requiring high sensitivity
with optimum signal-to-noise characteristics—as, for example, where
the electrical environment is especially noisy and there is a need
for high amplification of low signal levels.
Responding
only to the modulated carrier frequency, the 4078 rejects extraneous
voltages that can cause errors in DC systems. Excitation is fixed at
3 VAC (rms) at 3280 Hz.
Other
important 4078 features include
 |
remote
sensing and regulation of bridge excitation—eliminates errors
from temperature effects on cable resistance and yields consistently
stable ratiometric measurement, unaffected by possible power-supply
drift |
|
high
input
impedance preserves the validity of
factory calibration, prevents conversion of common-mode to
normal-mode signals, and eliminates remaining errors attributable to
cable resistance. Allowable cable length has virtually no
practical limits. |
|
user-adjustable
phase and symmetry controls for accurate calibration |
As
with most standard 4000 Series models, both active low-pass filtering and
user-selectable digital smoothing eliminate dynamic components arising
from vibration, power impulses, etc., that might prevent stable digital
conversion or control action (see Specifications).
Simple
two-point "zero and span" calibration is provided for the 4078's
input channel. In addition, a 59-kΩ, 0.1% shunt resistor
is supplied. You can use this resistor—or one or your own—to
apply an "equivalent input" for calibration purposes, when the
transducer's full-scale mV/V sensitivity is accurately known. The
calibration shunt may be switched in and out for either a positive or
negative up-scale reading by simple mnemonic
commands issued via the Interface Port or optional Model
10P80D Extended Keyboard. (Note that the special "MVV"
command used with the Model 4077 DC Strain Gage Instrument does not apply
to the Model 4078.)
|
Functions
Provided by the
MODEL 4078
"STANDARD
CONFIGURATION"
(for
a complete listing of the configuration, click
here) |
|
A
preprogrammed tare function may be activated by front-panel
button |
|
Via
front-panel buttons, you can call to display the
"live" tared input; the maximum (most
positive) value of that input since last reset; the minimum
(least positive) value of that input since last reset; or the
existing net difference between these maximum and minimum
values |
|
The "MAX" and "MIN" functions can be reset by a front-panel
button |
|
Each of the standard
seven predefined limit
zones of the tared input reading is tied to a specific nonlatching logic output |
|
The
4078's ±10
VDC analog output derives from the
tared analog input, and is initially scaled for 1 mV of output per
count |
|
For
a 4000 Series instrument based on both the Model 4078 and the Model
4040 Frequency Instrument, and dedicated to the measurement of torque,
rpm, and horsepower, see the Model 4K/HP
Horsepower Instrument.
For
a typical 4078 operation, see Monitoring
Engine Torque.
AC
Strain Gage Instrument Specifications [Top 
]
(Click
here for
4000 Series General
Specifications; see also
the statement
on Daytronic accuracy specifications)
|
|
Number
of Inputs |
One |
|
Input
Type |
Conventional
4-arm strain gage bridge, nominal 350 Ω or higher |
|
Input
Range (full-scale) |
0.75,
1.50, or 3.00 mV/V* |
|
Excitation
Supplied |
Regulated
3 VAC (RMS) at 3280 Hz; 75 mA (RMS) maximum |
|
Amplifier |
AC-coupled
demodulator with user-settable phase and symmetry controls |
|
Normal-Mode
Range |
±12
mV-AC (RMS) operating; ±8 VDC without instrument damage |
|
Common-Mode
Range |
±0.8
VDC operating; ±8 VDC without instrument damage |
|
Common-Mode
Rejection Ratio |
Infinite
at DC and 60 Hz; -80 dB at 1 kHz; -60 dB at 3 kHz |
|
Input
Impedance (Differential and Common-Mode) |
10 MΩ |
|
Offset |
Initial:
±3% of full scale
Vs. Temperature: ±0.005% f.s./°C
Vs. Time: ±0.002% f.s./month
|
|
Gain
Accuracy |
±0.025%
of full scale ± 1 count LSD, typical, following calibration** |
|
Gain
Stability |
Vs.
Temperature: ±50 ppm/°C
Vs. Time: ±20 ppm/month
|
|
Analog
Filtering |
|
Filter |
3-pole
modified Butterworth; -3 dB at 7.5 Hz; -60 dB at 60 Hz
|
|
Step
Response Settling Time (Full-Scale Output) |
To
1% of final value: 300 ms
To 0.1% of final value: 450 ms
To 0.02% of final value: 600 ms
|
|
*
Since channel zeroing is by digital techniques, no input balance control
is provided. The allowable input range, therefore, must include an initial
unbalance (which, in commercially produced strain gage transducers, is
negligible). Other transducers may have to be externally trimmed to
be used with the Model 4078, if zero unbalance exceeds 20% of full scale.
**
Initial (uncalibrated) inaccuracy may be as great as ±3% of full
scale. Maximum error that could occur upon replacement of the Model
4078 not followed by calibration is ±6% of full scale. |
|
