Enviro EA800 owner manual Power Supply / Sensor Voltage Selection

Sensors

Power Supply / Sensor Voltage Selection

In order to determine the power supply voltage necessary to ensure correct full-scale operation, it is necessary to identify all voltage drops within the current loop.

Figures 6 and 7 show an EA800 drop of 4.0 VDC. This value accounts for the voltage drop generated by connecting the 4-20mA sensor to the EA800 using 1000 feet of 22 AWG wire.

Now it is only necessary to identify the operating voltage range of the 4-20mA sensor, more importantly the minimum operating voltage. Once identified, the minimum operating voltage of the sensor can be added to the 4.0V voltage drop of the EA800 (+ wire) to determine the power supply voltage necessary to ensure correct full-scale operation.

Example:

■Assume that a 4-20mA sensor whose operating input voltage range is 10 – 30V has been selected for use. Therefore the minimum operating voltage of the sensor is 10V (Vsensor). When the 4.0V drop of the EA800 (and wire) is added, it can be determined that at least 14VDC is needed to power the loop.

■If the EA800 is connected to a 12VDC power supply, use of the sensor in this example requires an external power supply of at least 14V as shown in Figure 7.

It is important to not exceed the maximum operating voltage of the 4-20mA sensor, as specified within the sensor’s product specification.

The following formula provides the basis for the selection matrix shown in Table 7. Please use Table 7 to select either the proper sensor rating to be used with a known power supply, or select a power supply for a known sensor rating.

RL < (Vcc – x) .023 where:

■RL = Loop resistance of 200

■Vcc = Power supplied to EA800 or Aux Power Out

■X = Sensor voltage (max)

Table 7 4-20mA Voltage Select Matrix

Power Supplied to EA800	Vsensor (max.) [Maximum	Power Supplied to EA800 or	Vsensor (max.) [Maximum
or AUX. Power Out	sensor voltage rating]	AUX. Power Out	sensor voltage rating]
11 VDC	7 VDC	19 VDC	15 VDC
12 VDC	8 VDC	20 VDC	16 VDC
13 VDC	9 VDC	21 VDC	17 VDC
14 VDC	10 VDC	22 VDC	18 VDC
15 VDC	11 VDC	23 VDC	19 VDC
16 VDC	12 VDC	24 VDC	20 VDC
17 VDC	13 VDC	25 VDC	21 VDC
18 VDC	14 VDC	26 VDC	22 VDC

12 D-011-0152