Mounting and Wiring
Signal Wiring
V supply
Choose a supply that is compatible with the environmental requirements of your application. The supply voltage must be within the requirement of both the transmitter and the pulse input card. Typically a low cost 12 Vdc unregulated supply can be used in most applications provided in meets applicable regulatory requirements. 1k ohm termination resistors (RT) are built into the pulse frequency card. The voltage across the internal resistor must meet pulse frequency card requirements. The circuit in Figure 21 provides for a
1 k ohm load resistor and a 12 V supply. The actual pulse voltage seen across the pulse \ frequency input is divided by RT/(RL+RT) VSupply = 6 V. The VIH minimum pulse threshold voltage for the pulse input card is 3 volts. For a 1 k ohm load the minimum V supply will be 3 V (RL+RT)/ RT = 6V.
V return
The pulse / frequency cards pulse inputs are optically isolated from other circuitry but share a common isolated supply common. When multiple inputs are used the supply voltage returns will be connected to a common reference internal to the pulse frequency card. The pulse / frequency cards digital outputs are optically isolated from all inputs and each other.
RL
The maximum sink current specified by the pulse transmitter specifies the minimum load resistance. Typically RL is within the range of 100 to 100k ohms. A 1 k ohm resistor is typically recommended.
The transmitter often provides a selection for the pulse duration or width. The pulse input card internal R/C filtering will attenuate short pulse widths. Below is a table for filter and pulse width settings for several pulse frequency ranges.
Max Pulse Frequency
100kHz
10kHz
1kHz
100Hz
Typical Filter Jumper Setting
500 K Hz
100 K Hz
5 K Hz
5 K Hz
Pulse Width Range
2 uSec to 9 uSec
9 uSec to 90 uSec
180 uSec to 900uSec
180 uSec to 9mSec
(Vsupply = 12 Vdc, RL = 1 K ohm)
The minimum pulse frequency is 10 Hz regardless of the filter jumper settings.
The pulse frequency card input wiring requirements must be compatible with both the pulse frequency card and the transmitter manufactures specifications. A typical transmitter will specify the maximum supply voltage and the maximum sink current.
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