The Loop Leader PD688 is an Intrinsically Safe and Nonincendive, loop-powered, 1/8 DIN digital panel meter designed for hazardous process control applications. The fact that this meter is loop-powered means that there is no need to run additional, costly power lines into a hazardous area; the meter gets all of the power it needs from the 4-20 mA loop. The PD688 loop-powered indicator is built in a shallow-depth case with an FM Type 4X front and features loop-powered backlighting and a wide -30 to 65°C operating temperature range. It doesn't matter if it's indoors or outdoors, in bright sunlight or a dimly lit plant, or in an area that is wet, dirty, hot, or cold, the Loop Leader can go just about anywhere. The PD688 can be installed in just about any hazardous area environment under the FM, CSA, and ATEX standards.


  • 4-20 mA Input
  • 5-Digit Display
  • 0.6" (15.2 mm) LCD
  • FM Type 4X, IP65 Front
  • Shallow Depth Case 3.2" Behind Panel
  • 2 V Drop (5.7 V with Backlight)
  • Loop-Powered Backlight
  • Custom Engineering Units
  • Bargraph Display & Trend Arrow
  • Maximum & Minimum Display
  • Square Root, or Programmable Exponent
  • Non-Volatile Memory - No Battery Needed
  • Operating Temperature Range: -30 to 65°C
  • Intrinsically Safe & Non-Incendive
  • CE, ATEX, FM, and CSA Certified
  • HART Protocol Transparent


Display: Five digits: -99999 to 99999, 0.60" (15.2 mm) high, 7-segment, automatic lead zero blanking.
Engineering Units: 0.25" (6.4 mm) high, 14-segment.
Bargraph: 20-segment, 0% to 100% indication.
Trend arrows: Up and down trend indication.
Backlight: Bright orange (intensity varies with signal)
Display Update Rate: 2.5/second
Overrange: Display flashes 99999
Underrange: Display flashes -99999
Programming Method: Four front panel buttons
Noise Filter: Programmable from 1 to 199
Recalibration: Recommended at least every 12 months.
Max/Min Display: Max/min readings reached by the process are stored until reset by the user or until power to the meter is turned off.
Password: Programmable password restricts modification of programmed settings.
Non-volatile Memory: All programmed settings are stored in non-volatile memory for a minimum of ten years if power is lost.
Voltage Drop: 2.0 V max w/o backlight, 5.7 V max with backlight
Equivalent Resistance: 125 Ω @ 20 mA w/o backlight, 315 Ω @ 20 mA with backlight
Normal Mode Rejection: 64 dB at 50/60 Hz
Operating temperature range: -30 to 65°C
Allowable Temperature Range: -40 to 65°C* (see note below)
Storage temperature range: -40 to 65°C
Relative humidity: 0 to 90% non-condensing
Connections: Screw terminals accept 12 to 22 AWG wire
Enclosure: 1/8 DIN, high impact plastic, UL 94V-0, color: gray
Mounting: 1/8 DIN panel cutout required. Two panel mounting bracket assemblies provided
Tightening Torque: 4.5 lb-in (0.5 Nm) Screw terminal connections
Overall Dimensions: 2.45" x 4.68" x 4.19" (62 x 119 x 106 mm)
Weight: 5.7 oz (162 g)
Warranty: 3 years parts & labor


Input Range: 4-20 mA
Accuracy: ±0.03% of span ±1 count, square root and programmable exponent: 10-100% FS
Calibration: Scale without signal or calibrate with signal source
Calibration Range: User programmable over entire range of meter
Minimum Span: 0.40 mA between input 1 and input 2
Note: An Error message will appear if input 1 and input 2 signals are too close together
Input Overload: Over current protection to 2 A max.
Decimal Point: Up to four decimal places (d.dddd, dd.ddd, ddd.dd, dddd.d, or ddddd)
Function: Linear, square root, or programmable exponent
Low-Flow Cutoff: -99999 to 99999 (-99999 disables cutoff function)
Temperature Drift: 50 PPM/°C from -40 to 65°C ambient

*Below -30°C the LCD becomes less readable.

The Information contained in this document is subject to change without notice. Precision Digital Corporation makes no representations or warranties with respect to the contents hereof, and specifically disclaims any implied warranties of merchantability or fitness for a particular purpose.


Square Root Function

The square root extraction feature displays flow rate by extracting the square root from a differential pressure transmitter signal. The user selectable low-flow cutoff feature gives a reading of zero when the flow rate drops below a user selectable value.

Differential Pressure Flowmeter

  • Displays Flow Rate
  • User Selectable Low-Flow Cutoff
  • Only 2 Calibration Points Required

Example of Using Programmable Exponent Function

Programmable Exponent

The programmable exponent function is used to linearize the level signal in applications using weirs and flumes and display flow rate in engineering units.

4-20 mA Connections

Differential Pressure Flowmeter


Loop Leader Dimensions


  1. Panel cutout required: 3.622 x 1.772 (92 x 45)
  2. Panel thickness: 0.040 – 0.250(1.0 – 6.4)
  3. Mounting brackets lock in place for easy mounting

No software or accessories available for this product.

PD688 Loop Leader Loop-Powered Intrinsically Safe & Nonincendive Digital Panel Meter Price and Delivery Information
SKU Description In Stock Lead Time Price
PD688-0K0 Product Type: Loop Powered Meter
Inputs: Current (4-20 mA)
Backlight: Backlight
Outputs: None
Approvals: ATEX (IS), CSA (IS), CSA (NI), FM (IS), FM (NI), CE
2 days

Choose Your Options

FM Approved, CSA & ATEX Certified
Model No: PD688-0K0
In Stock (71)
$319.00 (each)