The Loop Leader PD684 is a loop-powered, 1/8 DIN flow rate/totalizer designed for demanding process control applications. The fact that this meter is loop-powered means that there is no need to run additional, costly power lines; the meter gets all of the power it needs from the 4-20 mA loop. The PD684 loop-powered rate/totalizer 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.


  • 4-20 mA Input
  • 5-Digit LCD, 0.6" (15.2 mm) High
  • Overflow Displays Total up to 8 Digits
  • Programmable Alternating Rate/Total Display
  • FM Type 4X, IP65 Front
  • Shallow Depth Case 3.2" Behind Panel
  • 2 V Drop (5.7 V with Backlight)
  • Loop-Powered Backlight Standard
  • Custom Engineering Units & Bargraph
  • Square Root or Programmable Exponent
  • Non-Volatile Memory - No Battery Needed
  • Maximum & Minimum Display
  • Operating Temperature Range: -20 to 65°C
  • Open Collector Alarm or Pulse Output
  • HART Protocol Transparent


Display: 5-digit LCD (-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)
Front Panel: FM Type 4X, IP65; panel gasket provided
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 nonvolatile 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 without backlight, 315 Ω @ 20 mA with backlight.
Normal Mode Rejection: 64 dB at 50/60 Hz
Operating temperature range: -20 to 65°C
Allowable temperature range: -40 to 65°C* (see note below)
Storage temperature range: -40 to 85°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 connectors
Overall Dimensions: 4.68" x 2.45" x 3.79" (119 x 62 x 96 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.
HART Transparency: Analog input will not interfere with existing HART communications on the wired 4-20 mA signal
Decimal Point: Up to 4 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

Totalizer Features

Total Display: 0 to 99,999 main total display plus 0 to 999 total overflow for a combined 8 digit total of 99,999,999.
Alternating Display: Display may be programmed to alternate between rate and total every 10 seconds.
Time Base: Seconds, minutes, hours, or days
Totalizer Conversion Factor: 0.0001 to 99999
Totalizer: Calculates total based on rate, time base of second, minute, hour, or day, and field programmable multiplier; stored in non-volatile memory upon power loss.
Totalizer Rollover: Total rolls over when total exceed 99,999,999.
Totalizer Reset: Manual reset or automatic with time delay, or disabled for non-resettable total applications.

Open Collector Output

Rating: Isolated open collector, 30 VDC @ 175 mA max.
Alarm Output: Assign to rate or total, high or low rate alarm.
Deadband: 0-100% of full scale, user selectable
Acknowledge: ACK button resets output and screen indication.
Automatic Reset: Alarm resets automatically when signal reaches the reset point.
Pulse Output: 250 pulses/sec max; pulse width: 3 ms, fixed. If the pulse output exceeds the maximum pulse output, counts are accumulated as pending and are not lost. One pulse per total increment, programmable from 0.0001 to 99999 (decimal point based on total selection).

* Below -20°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

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.

Example of Using Programmable Exponent Function

Alternating Rate & Totalizer Display

Press Enter/ACK button to alternate between rate and total or program the totalizer so the display automatically changes between displaying rate and total every 10 seconds. This feature is particularly useful if the meters are mounted inside a NEMA 4X or an explosion-proof enclosure.

Alternating Rate and Total Display

Total & Overflow Display

This feature allows the PD684 & PD689 to display total values up to eight digits. This sample shows a total of 68,923,684.

Display Showing Total and Overflow

Alarm Condition

After an alarm tripped simply press the ACK button for 3 seconds to acknowledge the alarm or wait for the alarm to reset automatically.

Alarm Trips and Acknowledged Shown on Display

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

Choose Your Options

Configurations other than those specified above are available at a $250 adder. Consult factory for desired model number and price.

Why you should buy:

  • Loop-Powered
  • 1/8 DIN Panel Mount
  • NEMA 4X/IP65 Front
  • Rate/Totalizer