The Problem:
A control system populated with devices that have simple I/O cards requires bi-directional digital control feedback. The System Designer is constrained by the need to keep costs minimized and avoid the investment in any high speed counter card, custom controller or higher order PLC.

The Solution:
Simple bi-directional feedback can be supplied via a "Pulse and Direction" encoder solution. In this case one channel of the encoder supplies a pulse count and the other channel runs either high or low, depending on direction. Encoder Products Company has long offered this solution in our Model 715 Cube. For applications requiring a through-bore or hollow-bore package, we also have available our Model 260 with Optional SPEC685. In this case, the SPEC685 designator provided quadrature signals on both A and B channels, with a directional pulse on the "Z" channel; Z "high" = CW shaft rotation. Z "low" = CCW shaft rotation.

Facts About Ethernet Cable
There are different types of cable used for Ethernet applications. Standards (ANSI/TIA/EIA) dictate the rules that must be applied when using Ethernet cable:

• A maximum of 100 meters of cable that includes: 90 meters of (solid conductor) horizontal cable and two, 5 meter (stranded conductor) patch cables to connect equipment to the backplane.
• Directly connect 30 meters of stranded cable.

Cable may be shielded or unshielded, stranded or solid. The choice of which cable type to use is dependent upon noise (electromagnetic interference) and distance of the cable run. The following scenarios will aid in this decision:

• If the cable is exposed to low noise and short distances (<30 meters), stranded, unshielded twisted pair cable should be used.
• If the cable is exposed to high noise and short distances (<30 meters), stranded, shielded twisted pair cable should be used.
• If the cable is exposed to low noise and long distances (>30 meters), solid, unshielded twisted pair cable should be used.
• If the cable is exposed to high noise and long distances (>30 meters), solid, shielded twisted pair cable should be used.

Also, if the application involves any kind of movement, stranded conductors should be used. If the application is static (requires no movement), solid conductors are the appropriate choice. Though this is only a general outline, it should help alleviate some confusion around specifying cables. Please refer to ANSI/TIA 568-C for the complete standards and guidelines.

Typical Starter / Contactor Configuration
Most Solid State Starters can be configured to operate with an inline contactor or bypass contactor. Typical one line diagrams for the power section are as follows:

The Reduced Voltage Starter will have minimal line voltage leakage on the leads of the motor. As with all solid state equipment, removing and tagging of an air gap device is required for safety before servicing the equipment.

Choosing a Sensor for Tank Level Application?
Often in level applications a pressure switch/transmitter can be used to determine tank level, if the tank is vented to atmosphere and the pressure sensor is mounted at the bottom of the tank. So how do you know what range sensor your customer would need? Simple. You need to know the height of the tank. Head pressure is what we are measuring so it doesn't matter if tank is 3' in diameter or 300', only the height is important. For example, if your cusotmer has a 20 ft tall tank you would convert feet to inches.

20ft * 12in/ft = 240" of water
1 psi = 27.7" of water

240"of water * 1 psi/27.7"of water = 8.6 psi so a sensor with a 0-14.5 psi range would work.

Choosing a Temperature Transmitter for your application
Perhaps the most fundamental consideration when specifying a temperature transmitter is the environment in which it will be installed. If the distance between the sensor measurement and the control room is relatively short and free of plant electrical "noise", temperature transmitters can be inexpensively installed in the control room, with sensor extension wires leading to them. These transmitter configurations are called DIN-style or rail- mount housings. For economy reasons, multiple high-density DIN-style transmitters are installed on a mounting rail in a multi-unit protective enclosure, and are powered by a common power supply.

Variable Frequency Drives With Multiple Motors
Care should be used when applying an inverter in a multiple motor application.

• Motors must be the same HP, Nema design, RPM, frame and voltage rating and preferably from the same manufacturer.
• Never switch a motor on and off from the output of a drive without first stopping the inverter.
• An output line reactor is recommended to help minimize the effects of multiple motors using one drive. Refer to the drawing for placement of the line reactor.
• The inverter should be sized by totaling the FLA of the motors and multiplying by 1.1, then selecting a drive that has a rating that meets or exceeds this FLA.
• Each motor must have its own Thermal Overload Relay and branch circuit protection (NEC Code).

What is Conductivity?
TURCK's FCMI flow meter has a fluid conductivity spec of 10 micro-Siemens or greater. What does that mean? Conductivity of a fluid is that fluid's ability to carry a charge. Conductivity is the inverse of resistivity which is sometimes easier to measure. Generally, for a fluid to work with the FCMI it needs be to conductive and in essence water based. DI-water, ultra pure water, oils, and highly concentrated acids or bases are not conductive.

What is a micro-Siemen anyway?

1 Seimen = 1/ohm = 1 mho or inverse ohm.

This unit stems from the fact the resisitivity measeured ohms is the inverse of conductivity.

A micro-Siemen is 1/ohm x 10^-6 ( a really little Siemen).

Protection Against Transient Voltage Spikes:
Power Filters & Transient Voltage Suppressors are very cheap PLC system insurance. Power filters protect your PLC system from noise and voltage spikes on the incoming power lines. Be sure that all devices in your system (PLCs, DC power supplies, etc.) are powered from the load side of the power filter. Transient Voltage Suppressors will drastically reduce voltage spikes that occur when de-energizing inductive loads.