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Tech Note 113: CMCP420VT(T) Compliance Last Updated: 05/10/2017 |
Note: The DC Supply Voltage range is: +18 to +36Vdc (See the application recommendations discussed above and note the limitations for Vs = +18Vdc) Specific compliance: RLmax for any given loop supply voltage can be calculated from the following equation as follows: RLmax = (Vs – 14 – Vd) / .020 (Note: The equation for the old black terminal unit was approximately (Vs - 14 - Vd) / .032) RL = Load Resistance Vs = DC Supply Voltage at the +V terminal. Vd = Display Voltage: 5.0 Vdc for LED, 2.0 Vdc for LCD, 0.0 Vdc for no display. The recommended RL for most installations is: Either 100 or 250 Ohms @ Vs = +24 Vdc at the +V terminal, with or without an LED or LCD display. Use the above RL equation to determine the required minimum supply voltage for a given loop load. Re-arranged to determine supply voltage, that equation becomes Vs = ((RL x .020) +14 +Vd) Ex: To drive 600 ohms with an LED display in the loop would require a minimum supply voltage of +31.6 Vdc. Vsupply min = (600x.020)+14+5 = 31.6 Vdc. Note: STI uses 23 mA for certification max current purposes. In practice the unit is limited to 21 mA. Anything over that indicates there is probably a problem with the unit. The older style (Black terminal) unit cycled its output current between 32mA and some lower value during power up. The latest version (Green Terminal) does not does not do this. It goes to approximately 21.5 mA at power application and then settles to the current reading. This takes a few seconds but it does not latch unless the RL and supply values from the equation are exceeded. |