Omega Speaker Systems RH/Temperature Transmitter HX93A - Manual (Page 6)

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HX15AV-W Wall mount “High Ambient Temperature” application
RH/Temperature transmitter (dual 0 to 1 Vdc Output)
HX15AC-W Wall mount “High Ambient Temperature” application
RH/Temperature transmitter (dual 4 to 20 mA Output)
HX15AV-D Duct mount “High Ambient Temperature” application
RH/Temperature transmitter (dual 0 to 1 Vdc Output)
HX15AC-D Duct mount “High Ambient Temperature” application
RH/Temperature transmitter (dual 4 to 20 mA Output)
3. Theory of Operation
A 4-20 mA loop is a series loop in which a transmitter will vary the
current flow depending on the input to the transmitter. In the HX93A
and the HX93DA Series the amount of current allowed to flow in the
loop will vary depending on the relative humidity or temperature being
measured by the sensor(s). 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 loop resistance in the sum of the
measuring instruments and wire used. The maximum allowable loop
resistance for the HX93A or HX93DA to function properly is found by
using the following formula:
For HX93A
Rmax = (power supply voltage – 6 volts) ÷ .02 amps
EXAMPLE: (When using a 24 Vdc power supply).
Rmax = (24 – 6) ÷ .02 amps = 900 ohms max loop resistance
For HX93DA Rmax = (power supply voltage – 12 volts) ÷ .02 amps
EXAMPLE: (When using a 24 Vdc power supply).
Rmax = (24 – 12) ÷ .02 amps = 600 ohms max loop resistance
Figure 1 - Basic Transmitter Set-up With Current Loop Output
TB1
TB2
45%RH
24V
23 °C
DPi8 Panel Meter
PSU-93
+
+
+ –
–
–
DPi8 Panel Meter
3
HX93A, HX93DA SERIES
RH/Temperature Transmitter
continued from page 1