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Flexible System Controller (FSC)

Fuel System Controller

Programmable Logic Controller

Installation Instructions

The FSC-120 is a general purpose programmable logic controller that is
programmed with Function Block logic. A single FSC can be used to control a
process, or multiple FSC’s can be networked together for coordinated
distributed control.

The most common application of the FSC is to monitor and control emergency
generator fuel oil supply pumping and storage systems.
Applications include:


  • Duplex transfer pumping skids
  • Day tank level control
  • Distribution piping Leak Detection
  • Multiple Main Tank motorized selector valve control
  • Main Tank filtration, water separation, and chemical injection
  • Tank truck off-loading pumps
  • Boiler burner oil pumping skids

Instruction Manual Scope:
This manual describes the FSC-120 controller hardware.
The application specific control logic is described elsewhere.
The FSC_Draw personal computer based logic creation/editing software
is described elsewhere.


Size 10.61h x 3.50w x 5.18d
(4) 0.17 dia. mounting holes in 10.11 x 2.40 pattern
Weight 5.5 lbs

Operating 32 to 131 F (0 – 55 C)
Storage -20 to 150 F ( -28 to 65 C)
Humidity 5 – 95% (non-condensing)
Enclosure Nema1
Power 120 Vac +15/-20%, 40VA, 50/60Hz
Discrete Inputs 24 channels
120 Vac, 12 mA typ., >70Vac = ON, Relay Outputs 10 channels
Ch. 1-5: SPST NO, 2A/250Vac each channel
One ‘common’ for all 5 channels
Ch. 6-10: SPDT, 10A, ½ hp 120/250 Vac
Analog Inputs 8 channels
4-20mA input, 100 ohm input resistor
0.2% accuracy, 13 bit resolution
22Vdc / 30mA supply for each channel
(the control logic enables/disables each 22Vdc supply)
Analog Outputs 3 channels
4-20mA, 800 ohm max loop resistance
0.2% accuracy, 13 bit resolution

Com0 Reserved for Touch Screen Interface
RS485, Modbus RTU, Device = 1 for all Nodes, 38.4k baud, 8/1/N
DC common connected to FSC DC common, but isolated from frame ground.
OIT-4k2 power output: 24Vdc / 180mA steady state / 250mA start-up
Com1 Shared Port for USB interface and RS485/RS232 interface.

Only one is active at a time, When USB is connected to a PC RS485/232 is auto disabled.
USB: USB 1.x, B socket, used for logic upload/download via FSC_Draw
RS485/232: Configured by Logic, reserved for future software upgrades, not currently active.
DC common connected to FSC DC common, but isolated from frame ground.
NodeNetA Node-to-Node Communications only. Redundant Auto Fail Over: A->B or B->A
Isolated RS485, Custom Protocol, 38.4k baud

NetA data & common is isolated from: NetB, FSC DC common, and FSC frame ground.
NodeNetB Node-to-Node Communications only. Redundant Auto Fail Over: A->B or B->A
Isolated RS485, Custom Protocol, 38.4k baud

NetB data & common is isolated from: NetA, FSC DC common, and FSC frame ground.
Firmware Upgradeable via SD Memory Card (must be

The FSC-120 is designed to be mounted inside an
enclosure which provides environmental protection.
The FSC-120 ambient temperature must be in the 32-
131F range during normal operation. The mounting
location must be free from excessive vibration.

The FSC-120 should be mounted vertically for proper
cooling. See the diagram for overall dimensions and
mounting hole locations.

Leave clearance room above and below the FSC-120 for
cooling and to provide easy maintenance access to the
USB port, SD card socket and for fuse replacement.


All panel and field wiring should conform to National and
Local Codes. Typically the NEC (National Electric Code)
applies to field wiring, while NFPA79 and UL508A applies
to panel wiring.

Connect the AC power ground to both the case ground lug
on the top of the enclosure and also to the “G” terminal on
the terminal strip.

AC Ground is isolated from all DC Common (-) terminals.
Terminal Blocks

All Field Wiring terminals are separable, and plug-in to the PC board. This allows rapid board level replacement
without disconnecting individual field wires. Verify that the terminals are inserted properly before applying power.
The AC line voltage terminals are numbered N, L, and 1 thru 45.

Terminals 26-45 are for the relay output contacts and can have either AC line voltage or DC low voltage wiring.
These terminals accept 24 – 12 ga. wire and should be tightened to 4.5 in-lb.
The DC low voltage terminals are numbered 101 thru 148.

These terminals accept 24 – 12 ga. wire and should be tightened to 2.2 in-lb.

DC Shielded Cable
All 4-20 mA Input and Output wiring should be 22 gauge minimum, 85% shield (min.), and have twisted pairs (Belden
8737 or equal). 100% foil shielding is preferable if available.

The shields of all 4-20 mA / 0-5 Vdc cables should be connected at one end only, as shown on the drawings that
follow. Generally, the shield is connected to the DC common of the Power Supply that is powering the signal. All
shield foils, and shield wires should be insulated (taped or heat shrink) to prevent accidental connection to earth or
power ground. Shields connected at both ends, or unintentional second grounds can actually add extra noise to a
signal instead of reducing noise. To prevent noise pick-up, shielded cables should never be run in conduits or trays
with AC wiring (any voltage). Ignition transformer and variable frequency drive AC wiring is particularly noisy and
should be kept separated from all DC signal wiring.

RS485 Communications Shielded Cable

All RS485 field wiring should use Belden 3106A, or equal, 3 wire shielded cable with 1 low capacitance twisted pair,
plus 1 DC common conductor. AC versus DC wiring physical separation. To reduce electrical noise interference all panel and field AC wiring should be separated from all panel and field DC wiring. AC and DC field wiring should not be run in the same conduit.


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