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Tank Gauging and Overfill Prevention etc.

2000 Absolute Digital Transmitter
2000 Absolute Digital Transmitter


The GSI-2000 Absolute Digital Transmitter provides transmission of mechanical tank gauge data and I/O from tank side to a communication interface or host system.


Theory of Operation

The transmitter mounts to a mechanical tank gauge, through a coupling assembly, and uses the direct linear input movement of the gauge to convert to a digital level output. An RTD connected will supply the temperature of the tank product. The Absolute Digital Transmitter consists of three major components:

  • Transmitter housing
  • Encoder (English Fractional, 16ths or Metric, mm)
  • Transmitter Board


Transmitter Housing

This is an explosion proof (NEMA 7) cast aluminum housing with wiring nipple assembly and J-condulet for field wiring terminations and optional surge protection. The transmitter housing is mechanically designed to couple directly to a GSI, Protectoseal, Motherwell or Varec mechanical tank gauge. With an optional coupling box, the transmitter housing will couple with various other mechanical tank gauges, such as L & J, Whessoe, etc.


Transmitter Encoder

GSI designed the 2000 Encoder to be the most reliable and accurate encoder on the market. With larger and thicker trace and two-way control of each contact brush.  The GSI 2000 Absolute encoder has the lowest MTBF and requires less maintenance than any other encoder on the market over the last 30+ years.

The 2000 eliminates problems found within other manufacturers’ brush and optical (absolute & non-absolute) encoders. Some manufacturers’ products still include parts such as Geneva gears, Two zero points on their Inch disk, one direction brush control, reflective code disks and optical diodes, non-stainless steel gearing, hall effect encoders, etc. that are more maintenance intensive. The GSI 2000 is an Absolute encoder, if it losses power and is repowered the level indication remains the same.  If a non-absolute encoder losses power (battery) it loses the level prior to power loss. Consequently, non-absolute transmitters have been known to have caused major spills (Overfill).


API Standards

As for API Chapter 3.1A and 3.1B, the manual reference hand line used for verification of automatic tank gauges is in 1/16” increments.  The mechanical tank gauges also measure in 1/16” increments.  If a manufacturer claims 1/32” or 1/64” from a mechanical tank gauge or transmitter it’s purely a marketing ploy and not verifiable accuracy.  They need to look at the mechanical Hysteresis is most mechanical tank gauges and the transmitter encoder before making these claims.


Transmitter Board

The 2000 Absolute Digital Transmitter supports a number of protocols and topologies for new applications or for integration and retrofit of existing systems. For new applications please consult GSI on the required protocol and topology for the application.

For integration and retrofit applications GSI has transmitter boards designed to meet field power requirements, electrical standard, protocol, and communication topology of your existing system. GSI manufactures field proven transmitter boards to match open standards such as MODBUS RTU / RS485 or vendor dedicated protocols such as Enraf® BPM (GPU), Varec® Mark-Space / 48Vdc, L&J Technologies® Tankway /38-70Vdc, MTS® DDA, and other manufacturers’ forms of non-compliant MODBUS / 220Vac – 24Vdc.

Note:  GSI standard protocol is MODBUS RTU over an RS 485 bus


Applications When used with a Mechanical Tank Gauge

  • Liquid Level Measurement
  • Temperature Measurement
  • I/O
    7 Analog or Digital Inputs, 2 Analog Outputs, 2 Form C Discreet Outputs
    4 SPDT Switches


Functional Specifications:
Encoding Method:Absolute Direct Linear Geared Brush Encoder
Code Disk: Identical, 1/8” Thick, copper/nickel/gold plated disks
Brush Mount:Removable, Drawer Mounted Assembly
Brush Block:10 non-feathering, bi-directional (tracking) brushes on each side
Level Measuring Range:0 - 96 Feet or 0 – 29.999 Meters
Output Protocols: Transmitter cards are available for various electrical standards and protocols (most tank gauging manufacturers’ and industry standards are supported)
Output Data: Level, Temperature, Status, and Status Contacts
Discrete I/O: (Optional) 4 discrete inputs (Optical isolated) , 2 dry contact outputs
Spot Temperature Input: 3-Wire RTD, copper or platinum
Average Temperature Input: 100-ohm copper or 100-ohm DIN platinum Characterized copper elements. Variable # of elements based on tank height.
Temperature Range:-100F to +400F
Input Power:12Vdc, 24Vdc, 48Vac, 48Vdc, 110Vac, 220Vac, etc. (Dependent upon the electrical standard selected)
Voltage Range: ± 10%
Current Consumption: 10mA @ idle, 35mA @ transmit
Heater/Drain: (Optional) Requires independent conductors & power supply (1 Pair, 24 Vdc @ 6.0 Amp)
Performance Specification:Operating Temperature Range: 32F to 158F or (0C to 70C) without Heater/Drain Option
Operating Humidity Range:0 to 98% relative, non-condensing
Signal Rate:Mark-Space protocols: Low Speed/High Speed
ASCII protocols: 300 baud to 62.5 Kilobaud
Fiber Optic transmitter: 300 baud to 76.8 Kilobaud tested
Level Accuracy:± 1/16” (1mm)
Level Repeatability:± 1/16” (1mm)
Temperature Accuracy: ± 0.2 degree F
Limit Switch Rating: Style A: ¼ Amp 125 Vdc, ¼ Amp 250Vdc, 4 Amp 125Vac “L”or 11 Amp 1/3hp 125, 250, 277 VaC
Style B: ½ Amp 125 Vdc, ¼ Amp 250Vdc, 20 Amp 125 & 250 Vac 1 hp 125 Vac or 2 hp 250 Vac
Surge Protection:Clamps @ 20% “over-voltage”, Type varies by Protocol & Electrical Standard (Combinations of MOV’s, Gas Caps, Transorbs, & Inductors)
Physical Specifications:Enclosure Material: Cast Aluminum with Epoxy coating
Enclosure Type:Explosion-Proof; Class I, Division 1, Group C & D UL and CSA Approvals
Power & Signal Wires: 18GA, Twisted & Shielded (0-1000FT), # of Conductors varies based on electrical standard & Protocol selected (Typically 4-Wire or Two Fibers)
Size: 7-7/8” OD x 13-1/2”
Weight: 22 LBS (with single J-Condulet and Transmitter Enclosure)