Halytech
hydroSpider2 User’s Manual v1.23
Page 119
4-wire arrangement
4-wire 4-20mA sensors have a separate power loop and output loop. A diagram for connecting
sensors of this type to the hydroSpider is shown below.
NOTE: no external resistor is needed
when the 4-20mA input type is selected. These inputs contain
an internal resistor and are pre-calibrated.
Appendix H6.
Voltage output sensors
Voltage output sensors communicate their data by outputting a voltage level which changes based
on the sensor’s measurements. Either of the hydroSpider’s analogue inputs (AIN1 and AIN2) can be
used for connecting sensors of this type.
The hydroSpider’s analogue voltage inputs (AIN1 and AIN2) can produce readings for voltages
between 0V and 2.4V.
If the sensor output is a voltage outside of this range, then two external resistors (forming a resistor
divider) are often required to avoid the sensor going outside of the hydroSpider’s range. Some
common sensor ranges and their resistor values are given in the table below:
Sensor Range
Value of Rx
Value of Ry
0V – 2.4V
None required (short circuit)
Leave out (open circuit)
0V – 5V
1.2 kΩ 0.25W metal film
1 kΩ 0.25W metal film
0V – 10V
3.3 kΩ 0.25W metal film
1 kΩ 0.25W metal film
