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參數資料
| 型號： | 930 |
| 元件分類： | 模擬信號調理 |
| 英文描述： | SPECIALTY ANALOG CIRCUIT, DIP11 |
| 文件頁數： | 4/4頁 |
| 文件大小： | 209K |
| 代理商： | 930 |
A
4
CALEX
FaxFACTS:
201
1997
Model 930 Programmable Current Source
http://www.calex.com
2401 Stanwell Drive
Concord, CA 94520-4841
(510) 687-4411 Fax (510) 687-3333
Transducer Bridge Drive
A bridge circuit located a significant distance from the exciting
and measuring system can be effected by unknown and or
changing drive line resistance. This can be eliminated by
driving the bridge with a constant current. The following
equation is used to determine the transducer resistance. The
voltage across the bridge is determined by the transducer
resistance.
The transducer resistance, RG, when in the upper arm, is
determined by the following equation:
RG = r (
Ι x r - 3 Vo) / (Ι x r + Vo)
where r is the resistance of the 3 fixed arms of the bridge.
Ι
is the constant current drive, and Vo is the bridge output
voltage. If RG is in the lower arm of the bridge, the minus and
plus signs in the equation are reversed.
Resistance Temperature
Measurement (RTD)
RTD’s are used to make accurate and stable temperature
measurements as one arm of a Wheatstone Bridge. Although
the RTD is more linear than the thermocouple, it still requires
curve fitting for best accuracy. A bridge circuit produces a
non-linear output for a linear change and thus requires an
additional curve fit. A single RTD driven by a constant current
source eliminates the errors associated with the bridge
method, including variable line resistance, although 4 wires
are required.
The Model 930 is an excellent constant current source for this
application. The 930 scale factor is set by an external RS
value of 10,000 ohms, providing a full scale output of 100
microamp. This resistor should be a 0.1%, 25 ppm, metal film
resistor. The other resistor values shown in Figure 4 provide
a small adjustment range around a 100 microamp output
current. This low level of current minimizes RTD self heating
error and produces a voltage change of 38.5 microvolts per
degree across a standard 100 ohm RTD with an alpha of
0.00385.
The components shown in Figure 4 will provide a current
source with a stability of 0.02% per degree ambient, from 0
to +70°C.
If a copper RTD is being used, the current source is easily
changed to 500 microamps by replacing the 10 kRS with a
2000 ohm, 0.1%, 25 ppm stable resistor.
Slip-ring Application
Slip-rings are often required to interface across a rotating
boundary. As an example, consider a temperature or strain
measurement that uses a 100 ohm transducer. Used in a
bridge circuit, every 1 ohm of varying line resistance could
contribute up to 1% error for each line that crosses the slip-
ring interface.
By using the sensor as a single resistance element and
constant current excitation as in Figure 5, the errors due to the
slip-ring changing resistance can be eliminated. If the 100
ohm transducer required 10 mA of drive current, the Model
930 could be operated from a 15 Volt supply allowing the slip-
ring and line resistance to vary from zero ohms to 900 ohms
without effecting the drive to the transducer. This also
eliminates the curve fitting step required by non-linear bridge
circuit outputs.
The measurement path would, in most cases, contribute a
negligible error. A typical volt meter has 10 megohms input
resistance, so a 1000 ohm series resistance change due to
the slip-rings would contribute only 0.01% of reading error.
Voltage-to-Current Converter
A Model 930 can be teamed up with a Model 178
instrumentation amplifier to convert low-level transducer
bridge voltages to output currents compatible with process
control equipment. The Model 930 is connected for a voltage
input. The output current range can be selected by varying
the impedance between pins 10 and 11.
FIGURE 6.
FIGURE 5.
FIGURE 4.
Other Applications
Other applications include charging batteries at a constant
current rate, Hall effect sensors, microplating using the
electrolytic process, and testing gyro torquers.
相關PDF資料 |
PDF描述 |
|---|---|
| 930 | FEMALE, TWO PART BOARD CONNECTOR, IDC |
| 9310-50 | 1 ELEMENT, 30 uH, IRON-CORE, GENERAL PURPOSE INDUCTOR |
| 9310-40 | 1 ELEMENT, 15 uH, IRON-CORE, GENERAL PURPOSE INDUCTOR |
| 9310-36 | 1 ELEMENT, 10 uH, IRON-CORE, GENERAL PURPOSE INDUCTOR |
| 9310-34 | 1 ELEMENT, 8.2 uH, IRON-CORE, GENERAL PURPOSE INDUCTOR |
相關代理商/技術參數 |
參數描述 |
|---|---|
| 930 111-100 | 制造商:SKS KONTAKTTECHNIK GMBH 功能描述:PROBE-BLACK |
| 930 111-101 | 制造商:SKS KONTAKTTECHNIK GMBH 功能描述:PROBE-RED |
| 930 126-102 | 制造商:SKS KONTAKTTECHNIK GMBH 功能描述:PUSH BUTTON CROC.CLIP BLU |
| 930 126-103 | 制造商:SKS KONTAKTTECHNIK GMBH 功能描述:PUSH BUTTON CROC.CLIP YEL |
| 930 308-100 | 制造商:Hirschmann Electronics GmbH & Co Kg 功能描述:SCREW IN JACK BLAC 2MM *NIC* |
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