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34 UMC800 Controller Installation and User Guide Release F
4/01
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 (R
T
) 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 R
T
/(R
L
+R
T
) V
Supply
= 6 V. The V
IH
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 (R
L
+R
T
)/ R
T
= 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.
R
L
The maximum sink current specified by the pulse transmitter specifies the minimum load resistance.
Typically R
L
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 Typical Filter Jumper Setting Pulse Width Range
100kHz 500 K Hz 2 uSec to 9 uSec
10kHz 100 K Hz 9 uSec to 90 uSec
1kHz 5 K Hz 180 uSec to 900uSec
100Hz 5 K Hz 180 uSec to 9mSec
(Vsupply = 12 Vdc, R
L
= 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.