|
 The
Model 3570 DC Strain Gage Conditioner is a general-purpose instrument for
input of pressure, force, torque, weight, and other variables
measured by DC-excited strain gage transducers. It accepts a
single input from any conventional 4-arm strain gage bridge, nominal 120
Ω or higher, with a full-scale range of 0.75, 1.5, or 3.0 mV/V.
Optional bridge-completion circuitry is provided by the Model
10CJB-2, allowing input from a 2-wire 1/4-bridge, 3-wire 1/4
bridge, or 1/2-bridge gage configuration, as shown in Stress
Analysis Using External Bridge Completion.
Advanced
circuit design overcomes many of the errors traditionally afflicting the
strain gage measurement process, resulting in rock-solid digital
indication and noise-free analog output.
Other
important 3570 features include
 |
selectable
bridge excitation (nominal 2, 5, or 10 VDC) |
|
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 |
|
input
impedance in excess of 100 megohms 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. |
|
selectable
active low-pass filtering smoothes unwanted dynamic signal 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 3570's
input channel. In addition, a 100-kΩ, 0.1% shunt resistor
is supplied. You can use this resistor—or one of 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 via simple mnemonic
commands issued to the RS232/RS485
port or by means of logic-level command signals through the rear Analog
Input Connector.
A
third calibration technique for the 3570 involves application of the special
MV/V CALIBRATION (MVV) command through the RS232/RS485
Interface Port when both "mV/V" sensitivity and corresponding
full-scale rating of the transducer are known.
The
3570 offers all standard 3500 Series features,
including
|
selectable
digital smoothing |
|
custom
15-segment linearization |
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HI/LO
limit monitoring with logic I/O |
|
scalable
analog output |
|
analog
+peak capture |
|
automatic
tare offset |
|
digital
track and hold |
|
either single-node
(RS232) or multinode network (RS485) communications |
The
instrument can be completely set up and operated either through the
front-panel keypad or via simple mnemonic
commands received from an external computer or terminal through
the RS232/RS485 Interface Port.
For
typical 3570 operations, see the following
applications:
DC
Strain Gage Conditioner Specifications [Top 
]
(Click
here for 3500 Series General
Specifications; see also
the statement
on Daytronic accuracy specifications)
|
|
Input
Type |
Conventional
4-arm strain gage bridge, nominal 120 Ω or higher NOTE:
1/4- and 1/2-bridge gage configurations can be accomplished by means
of the Model 10CJB-2 Bridge Completion Card,
or by equivalent external bridge completion circuitry supplied by the
user. |
|
Input
Ranges (full-scale)* |
Nominal
Input Range |
Actual
Normal-Mode Input-Signal Voltage (Max.) |
Absolute
Maximum Overrange
(50%) |
Input
at which Display Reading Corrsponds to
"m" Term |
|
3.0
mV/V |
45
mV/V |
4.5
mV/V |
4.0
mV/V |
|
1.5
mV/V |
22.5
mV/V |
2.25
mV/V |
2.0
mV/V |
|
0.75
mV/V |
11.25
mV/V |
1.125
mV/V |
1.0
mV/V |
|
|
Excitation
Supplied |
Selectable
10, 5, or 2 VDC; 85 mA maximum |
|
Normal-Mode
Range |
±45
V operating; ±8 V without instrument damage |
|
Common-Mode
Range |
±0.50
V operating; ±8 V without instrument damage |
|
Common-Mode
Rejection Ratio |
-60
dB at DC; -90 dB at 60 Hz, 1 kHz, and 3 kHz |
|
Input
Impedance (Differential and Common-Mode) |
Greater
then 100 MΩ |
|
Offset |
Initial:
±0.025% of full scale
Vs. Temperature: ±25 ppm/°C
Vs. Time: ±10 ppm/month |
|
Gain
Accuracy |
±0.02%
of full scale ± 1 count LSD, typical, following calibration** |
|
Gain
Stability |
Vs.
Temperature: ±50 ppm/°C
Vs. Time: ±20 ppm/month |
|
Analog
Filtering |
|
Fixed |
2
kHz |
|
Selectable |
5-pole
filter with selectable low-pass corner frequency of 5, 10, or 20 Hz |
|
Frequency
Characteristics |
|
Corner
Frequency |
| Response
at . . . |
5
Hz |
10
Hz |
20
Hz |
|
-3
dB |
5
Hz |
10
Hz |
20
Hz |
|
-60
dB |
32
Hz |
65
Hz |
125
Hz |
|
|
Step
Response Settling Time (Full-Scale Output) |
|
Corner
Frequency |
| |
5
Hz |
10
Hz |
20
Hz |
|
To
1% of final value |
250
ms |
125
ms |
60
ms |
|
To
0.1% of final value |
400
ms |
200
ms |
100
ms |
|
To
0.02% of final value |
600
ms |
300
ms |
170
ms |
|
|
Peak
Capture |
Positive
analog peak, digitally held for indefinite display; minimum full-scale
input pulse duration is 6 msec (to 1% of full-scale accuracy), 12 msec
(to 0.1% of full scale accuracy), and 20 msec (to 0.02% of full-scale
accuracy); PEAK and TRACK modes controlled by front-panel button, rear-panel
logic input, or computer-port command |
|
Analog
Output***: See 3500
Series General Specifications |
|
Frequency
Characteristics and Step Response Settling Times |
After
(A) FIXED ANALOG FILTER or after (B) +PEAK in "TRACK" Mode: -3 dB at
2 kHz; -60 dB at 16 kHz; settling
time to 1% of final value: 0.6 msec; to 0.1% of final value: 0.75 msec; to
0.02% of final value: 1.25 msec
After
(B) +PEAK in
"PEAK" Mode: Settling
time to 1% of final value: 6 msec; to 0.1% of final value: 12 msec; to
0.02% of final value: 20 msec After
(C) SELECTABLE ANALOG FILTER: See Analog Filtering
(Selectable), above |
|
*
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 3570, if zero unbalance exceeds 20% of full scale.
**
Initial (uncalibrated) inaccuracy may be as great as ±0.05% of full
scale. Maximum error that could occur upon replacement of the Model
3570 not followed by calibration is ±0.1% of full scale.
***
When (1) the analog output scale is 100.0%, (2) the analog output offset
is 0.0%, and (3) the selected excitation is 10 V, then any of the
following inputs will result in an analog output of 5 V: an input
of 4 mV/V on the 3.0-mV/V range; an input of 2 mV/V on the 1.5-mV/V
range; or an input of 1 mV/V on the 0.75-mV/V range. |
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