NE5230, SA5230, SE5230

http://onsemi.com

11

What this means is that several instruments, such as a chart

recorder, a meter, or a controller, as well as a long cable, can

be connected in series on the loop and still obtain accurate

readings if the total resistance does not exceed 650

W.

Furthermore, any variation of resistance in this range will

not change the output current.

Any voltage output type transducer can be used, but one

that does not need external DC voltage or current excitation

to limit the maximum possible load resistance is preferable.

Even this problem can be surmounted if the supply power

needed by the transducer is compatible with the NE5230.

The power goes up the line to the transducer and amplifier

while the transducer signal is sent back via the current output

of the NE5230 transconductance configuration.

The voltage range on the input can be changed for

transducers that produce a large output by simply increasing

the current sense resistor to get the corresponding 4.0 to

20 mA output current. If a very long line is used which

causes high line resistance, a current repeater could be

inserted into the line. The same configuration of Figure 7 can

be used with exception of a resistor across the input and line

ground to convert the current back to voltage. Again, the

current sensing resistor will set up the transconductance and

the part will receive power from the line.

TEMPERATURE TRANSDUCER

A variation on the previous circuit makes use of the supply

current control pin. The voltage present at this pin is

proportional to absolute temperature (PTAT) because it is

produced by the amplifier bias current through an internal

resistor divider in a PTAT cell. If the control pin is connected

to the input pin, the NE5230 itself can be used as a

temperature transducer. If the center tap of a resistive pot is

connected to the control pin with one side to ground and the

other to the inverting input, the voltage can be changed to

give different temperature versus output current conditions

(Figure 8). For additional control, the output current is still

proportional to the input voltage differential divided by the

current sense resistor.

When using the NE5230 as a temperature transducer, the

thermal considerations in the previous section must be kept

in mind.

V

REMOTE

POWER

SUPPLY

NE5230

3

2

4

5

6

7

+

−

+

−

NOTES:

4mA

20mA

4mV

20mV

200

Figure 8. NE5230 remote temperature transducer utilizing 4.0 − 20 mA current transmission. This application

shows the use of the accessibility of the PTAT cell in the device to make the part, itself, a transducer.

10W