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Two-Wire, Current-Loop Process Indicator in NEMA-4X Housing

Two-wire, Current Loop Process Indicator
FM Intrinsic Safety Certification
Powered by 1-5, 4-20 or 10-50 mA Signal
2.5 V Max Voltage Drop
0.35 in (8.9 mm) Liquid Crystal Display
2,000-Count Zero Suppression or Elevation
100 to 2,000 Count Span Adjust
Selectable Dummy Right-Hand Zero
–40°C to +85°C Operation
Compact, 2.9 in Diameter Die-Cast Housing
Waterproof to 35 kPa (5 psi)
Shock Resistant to 55 g

1/2 EMT Conduit Fitting
1/2 NPT Pipe Fitting
Relay-Track Mounting Adapters
External Explosion-Proof Housing
Companion Current Transmitters

1 Year Warranty

Starting from Nov 30, 2018, the 508B Series will be discontinued. As an upgrade substitute, please check out the new TXUN temperature transmitter for details.

Model 508B is a two-wire current-loop indicator that is powered directly by a 1-5 mA, 4-20 mA or 10-50 mA process loop signal, with a maximum voltage drop of 2.5 V. No separate power supply connections are required. This reduces overall hardware and field wiring costs and provides immunity from most electrical noise encountered in process control environments. The electronics are isolated from the case.

The 508B provides extensive zero and span adjustment capability, so that it can read out directly in percent or in engineering units for process variables such as pressure, flow, temperature, or level. Its liquid crystal display provides 3 1/2 active digits, a selectable dummy right-hand zero, and four programmable decimal points. By changing two internal jumpers, the normal positive slope response of the 508B can be reversed, so that increasing the input decreases the reading.

Both span and zero are fine-tuned with precision multiturn potentiometers. These are accessible through holes in the die-cast cover, which are normally sealed with fluorosilicone plugs. Coarse zero and span steps are selected by removing the cover with attached electronics and changing plug-in jumpers.

All versions of the 508B are rated for operation from –40 to +85°C (–40 to +185°F) with specified accuracy. The case is made of die-cast metal and is waterproof to 35 kPa (5 psi). The electronics are firmly connected to the case top, so that the meter can withstand high vibration and shock. Mounting options include a male 1/2 EMT conduit fitting and a male 1/2 NPT pipe fitting in lieu of the normal rail or surface mount. These fittings eliminate the external screw terminals and provide a NEMA-4X rating.

FM intrinsic safety certification is standard. Intrinsic safety certification allows the 508B to be used in worst-case hazardous environments with no need for an explosion-proof housing, provided that an intrinsic safety barrier is used to limit the voltage and current that may be introduced in the hazardous environment.

FM certification (USA) is for Class I, II, III, Division 1, Groups A, B, C, D, E, F, G. The FM certification number is 2P1A7.AX (3610:2010).


Two external NEMA-7 explosion-proof and NEMA-4 waterproof, sand-cast, copper-free aluminum enclosures with corrosion resistance "safety-blue" polyester powder-coating for use in hazardous locations.
FM, UL, cUL Certification: Class I, Groups B, C, D; Class II, Groups E, F, G; and Class III, Type 4X.
Demko/ATEX Certification: Ex II 2 G D EEx d IIC

Option EPW3-ATEX is a single-height enclosure for one 508B loop-powered indicator.
Option EPW2-ATEX is a double-height enclosure for a 508B loop-powered indicator on top and a 500 Series isolated two-wire 4-20 mA transmitter on the bottom for indicating transmitter applications.
Available with two female 1/2 NPT pipe fittings, all required internal mounting hardware, and mounting flanges for a wall or bulkhead.

Signal: 1-5 mA, 4-20 mA or 10-50 mA (jumper-selectable)
Linear Range: 0.3 to 50 mA
Protection: Up to 200 mA forward, 1000 mA reverse
Forward voltage drop, max: 2.5 V up to 50 mA
Input Resistance: 50 ohm at 1-5 mA, 12.5 ohm at 4-20 mA, 5 ohm at 10-50 mA
Zero Adjust: –2,000 to +2,000 counts (4 jumper- selectable ranges plus fine adjustment)
Span Adjust: 0 to 2,000 counts with fine adjustment
NMR: 46 dB, 50/60 Hz
CMR: (meter to case) 120 dB, DC to 60 Hz
CMV: (meter to case) 700 Vp
RFI Susceptibility: Less than ±0.5% of span with conduit fitting or external explosion-proof housing in 10V/m field strength at 27 or 440 MHz


Maximum Error: 0.1% of span ±1 count 00 Zero tempco ±0.1 count/°C typical, ±0.2 count/°C max
Span Tempco: ±0.005% of span/°C typical, ±0.015% of span/°C max

Technique: Dual-slope, average-value
Polarity: Automatic
Integration Period: 100 msec
Read Rate: 2.5/sec

Type: 7-segment, LED
Height: 0.35" (8.9 mm)
Symbols: – (3 1/2 active digits plus one jumper-selectable dummy right-hand zero)
Decimal Points: Four positions, jumper-selectable
Overrange Indication: Three least-significant active digits blank

Operating Temperature: –40 to +85°C (–40 to +185°F)
Vibration: 0.06" (1.52 mm) double-amplitude cycled at 10-80 Hz
Shock: 55 g half-sine, 9-13 ms duration
Waterproof Pressure: 35 kPa max (5 psi)

Diameter: 2.9" (74 mm)
Height, Including Barrier: 1.9" (48 mm)
Weight: 14oz (400 g)

508B-1: 3-terminal barrier strip with #6 screws
508B-2: 1/2" EMT male conduit fitting with two 0.3 meter #18 stranded wires
508B-3: 1/2" NPT male pipe fitting with two 0.3 meter #18 stranded wires

• Surface mount with four #6 rear-entry screws from backside of bulkhead.
• Snap mount into 2.50" (63.5 mm) relay track.
• Surface mount with two #8 front-entry screws. Requires MAT1 adapter plate.
• Snap mount into 2.75" (69.9 mm) or 3.00 in (76.2 mm) relay track. Requires MAT1 adapter plate.
• Snap mount into DIN relay track. Requires MDT1 rail clamp.
• Push mount into explosion proof-housing EPW3-ATEX.

1/2" EMT male conduit fitting
508B-3: 1/2" NPT male pipe fitting

A Model 508B process-loop indicator may be added to an existing 4-20 mA or 10-50 mA installation. No additional wiring is required, since the meter is powered directly by the current loop.

All dollar amounts on this site are shown in US currency.

Keywords: Two-Wire, current-loop, process indicator, NEMA-4X Housing, current loop indicator, 508B, FM certified, explosion proof housing, intrinsic safety

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