2808B DP Transmitters / 1B-3
Figure 1B-3 - Simplified Diagram
Implanted on the sensor's micro-machined surface are four strain gauge resistors connected
in a bridge configuration. This circuit, which is powered by a constant current supply on the
amplifier board, produces a millivolt output that is equal to the difference between the two
pressure inputs.
Output of the sensor circuit is wired to a high-gain, linear amplifier that converts the
millivolt signals to a 4-20 mA current output. Figure 1B-3 shows the Transmitter output
wired to a typical external loop circuit. This circuit uses a 250-ohm load resistor and a 24 V
dc power source. 4-20 mA amplifier current flowing through the load resistor produces a 1-5
V input signal for the external device.
Amplifier circuittry includes a fine-gain and fine-offset potentiometer for performing minor
calibration adjustments. Transmitters also include internal coarse zero and coarse span
switches for more extensive range conversion.
1B.3 IDENTIFYING TRANSMITTER OPTIONS
A data plate affixed to the transmitter body lists the model number, serial number, and
instrument range. To identify the features and options furnished with your model, refer to
the complete
model number contained in the sales order. This number includes a sequence
of suffix numbers that are identified in Table 1B-A.
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