PHD User Guide
13
Internal to product
Sensor Power
Resistive Sensor
Pull-up
Resistor
Active Sensor
Analog Input
Analog Input
Figure 3.4. Analog input ground shift connection for sensors that have dedicated ground wires
3.3.2.
PHD70 digital input capabilities
The PHD28 and PHD50 displays have analog inputs, but they can be configured as digital inputs by
programming the voltage threshold in the Lua scripting tool to make them digital.
•
The PHD70 has up to 10 traditional active high digital inputs.
•
The PHD70 digital inputs can also be configured as low power digital outputs.
The following table provides specifications for the PHD’s digital inputs:
Digital input specifications
Item
Min
Nom
Max
Unit
Input voltage range
0
32
V
Pull-down resistance
26.2
kΩ
Pull-up resistance (to 4.3V min / 5V max)
1.2
kΩ
Negative threshold
1.545
V
Positive threshold
4.008
V
Cutoff frequency (hardware)
1590
Hz
Over-voltage
36
V
Wetting current (through pull-up)
4.3
mA
3.3.2.1.
Active-High Digital Input Connections
A digital input is typically connected to a switch that is either open or closed.
•
When an active-high switch is open, the pull-down resistor ensures that no voltage exists on the
input signal, which will be interpreted by the PHD as inactive.
•
When the switch is closed, the input is connected to battery voltage, which will be interpreted by the
PHD as active.
For an input that is active-high
•
It must be connected to battery power so that there is a battery connection when the state of the
input changes.