Section 3 – Theory of Operation and Electrical Connection
3.1.1 Theory of Operation
A 4 to 20 mA loop is a series loop in which a transmitter will vary the current
flow depending on the input to the transmitter. In the HX92B the amount of the
current allowed to flow in the loop will vary depending on the relative humidity
being measured by the sensor. Some advantages of a current output over a
voltage output is that the signal measured is less susceptible to electrical noise
interference, and the loop can support more than one measuring instrument as
long as the maximum loop resistance is not exceeded.
A typical application utilizing a current loop will normally consist of a power
supply, the transmitter and a meter, recorder or controller to measure the
current flow. The maximum allowable loop resistance for the HX92B to function
properly is found by using the following formula:
Rmax = ((power supply voltage – 4) ÷ .02)
EXAMPLE: (When using a 30 Vdc power supply).
Rmax = ((30 – 4) ÷ .02) = 1,300 ohms max loop resistance
All electrical connections and wiring should be performed by a
suitably trained professional only.
Follow the electrical connection diagram shown in figure 3-1 and 3-2 below to
set up your Relative Humidity Transmitter.
Figure 3-1. Voltage Output Connection Diagram
3-1
Theory of Operation and Electrical Connection
3
POWER IN
R/H OUTPUT
GND
GND
CHASSIS
1
2
3
4
5
+
–
+
–
POWER SUPPLY
9-30 Vdc
(12-30 Vdc FOR
0-10 Vdc OUTPUT)
TB1
INTERNALLY CONNECTED
0-1 Vdc
0-5 Vdc
0-10 Vdc
CAUTION:
