Sensaphone Express II - Manual (Page 19)

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Chapter 3: Inputs
CHAPTER 3: INPUTS
Express II comes standard with 8 universal inputs. The input capacity may be expanded in
additional sets of 8 inputs. There are 5 slots, offering a total of 40 possible universal input
channels. All the inputs—the 8 standard and the expanded sets—can be configured to accept
the following type sensors:
• Normally closed dry contact (digital)
• Normally open dry contact (digital)
• Pulse count
• 4–20 mA (analog)
• 0–5 Volts (analog)
• Temperature
• 2.8K F thermistor (analog)
• 2.8K C thermistor (analog)
• 10K F thermistor (analog)
• 10K C thermistor (analog)
• Time accumulator
The standard 8 input terminal block is located to the right of the built-in keypad in the first card
slot. Above the terminal block are a row of 8 LEDs that indicate the status of the inputs to on-
site personnel.
HOW THE INPUTS WORK
Express II reads the value of each input by measuring the voltage across the input and the
common terminals. When the shunts are positioned for a specific type of sensor, Express II
uses a different circuit to measure the appropriate reading for that sensor. The common Express
II sensor types follow:
Dry Contact—These digital sensors can be either Normally Open or Normally Closed
(designated N.O/N.C). If a normally open sensor becomes closed, a contact occurs. This causes
an alarm. Conversely, if a normally closed sensor becomes open, the contact disappears, and
this condition causes an alarm. Typical dry contact sensors include magnetic reed switches and
water detection sensors. An example would be a security system where a N.C. magnetic switch
opens as a window is raised.
Pulse Count—This configuration will allow the input channel to count pulses. A typical pulse
count sensor is a flow meter that uses a turbine to measure flow by accumulating pulses. Max
pulse rate for this configuration is 1Hz. Compatible with mechanical relays, open drain and
open collector transistor devices.
4–20 mA—This sensor configuration connects the input signal to a 237 Ohm load resistor. This
allows Express II to measure the current at the input. Any powered or unpowered sensor that
puts out 4–20mA can be wired. Any input range can be specified by the user. Typical sensors
include pressure gauges, analog flow meters, and temperature gauges. Input resolution is 12
bits.