Campbell CURS100 Uživatelský manuál stáhnout pdf (Strana 15)

User Manual

Figure 4-7. 4-wire with external power

5. Sensor and Programming Example

In this example, the input voltage range, and the multiplier and offset values are

calculated for a 4 to 20 mA output pressure transducer. Examples showing the

differential measurement made on Channel 1 are then given for the CR1000,

CR9000(X), CR10(X), and 21X dataloggers; programming for the CR800,

CR850, CR3000, and CR5000 is virtually identical to the CR1000.

5.1 Voltage Range

The voltage range on which to make the measurement should be the smallest

range that will accommodate the maximum signal the sensor will output. Using

the smallest possible range will give the best resolution.

The voltage across the resistor, V, is equal to the resistance (100 ohms) multiplied

by the current, I.

V = 100 I

The maximum voltage occurs at the maximum current. Thus, a 4 to 20 mA

transducer will output its maximum voltage at 20 mA.

V = 100 ohms  0.02 A = 2 V

An output of 2 volts is measured on the ±2500 mV range on the CR800, CR850,

CR1000, and CR10(X), or on the ±5000 mV range on the 21X, CR3000, CR5000,

or CR9000(X).

5.2 Calculating Multiplier and Offset—An Example

The multiplier and the offset are the slope and y-intercept of a line and are

computed with Ohm’s law and a linear fit.

For example, measure a current loop transducer that detects pressure where the

sensor specifications are as follows:

Transducer range — 200 to 700 psi

Transducer output range — 4 to 20 mA

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Campbell CURS100 Uživatelský manuál Strana 15