Model: PDS178X2

PDS178 Watchdog Scanner Temperature & Process System

Product Type: Watchdog 8 Channel Temperature Scanning System with Trident X2
Inputs: Thermocouple, RTD
Output Options: 2 Relays
Display Category: LED, Single Line, Sunlight Readable, Large Display
Display: 1.2" High, 4 Digits, Red LED
Approvals: None
Warranty: 3 years
Product Family: PDS178
Product Category: Annunciators & Scanners, Enclosures
Product Application: Temperature, Process, Enclosures
Applicable Meter Types: C

The PDS178 Watchdog Temperature Scanning & Alarming System brings together a popular combination of Precision Digital products: the Trident meter, the Minimux II scanner, and the PDA2821 NEMA 4X enclosure. The scanner automatically switches between up to eight (8) input signals (4-20 ma, ±10 V, TC, or RTD) and sends them to the Trident meter for display. Signal switching is done via DPST reed relays. The Watchdog can be used in a variety of temperature and process monitoring applications. A very common application for this system is to monitor bearing temperatures. The Trident meter included with this system is available with standard 0.56" (14.2 mm) high LED digits or large 1.2" (30.5 mm) high LEDs.


Trident Temperature & Process Meter

  • 4-20 ma, ±10 V, TC & RTD Inputs
  • 4-Digit Display
  • Two Relays for Alarm Signal to PD138
  • NEMA 4X, IP65 Front
  • Sunlight Readable Display

Minimux II Temperature/Process Scanner

  • 8 Inputs per Unit
  • Thermocouples, RTDs, and Process inputs
  • Adjustable Dwell Time for Each Channel
  • Independent Alarm Input for Each Channel
  • First-Out Alarm Indication
  • Alarms Indicated by LEDs, Built-in Horn,
    and Relay
  • Built-in 85 dB Horn with Silence Pushbutton
  • Stop-on-Alarmed Channel (Field Select)
  • Sunlight Readable Indication
  • NEMA 4X/IP65 Front

Plastic NEMA 4X Enclosure

  • NEMA 1, 4, 4X, 6, 12, and 13, IP66
  • Wall Mountable

Note: These specifications apply to the entire product series and may contain information that is not relevant to this particular model number.

PD765 Trident Meter

Display: Trident: 0.56” (14.2 mm); Trident X2: 1.20” (30.5 mm) red LED, 4 digits (-1999 to 9999)
Display Intensity: Eight user selectable intensity levels
Front Panel: NEMA 4X, IP65; panel gasket provided
Programming Methods: Four front panel buttons, cloning with Copy feature, PC with MeterView or LabVIEW software, and Modbus registers. Certified LabVIEW driver available.
Noise Filter: Programmable 2 to 199 (0 will disable filter)
Display Update Rate: Process/RTD: 3.7-5/sec; TC: 1.8-2.5/sec
Overrange: Display flashes 9999
Underrange: Display flashes -1999
Recalibration: All inputs are calibrated at the factory; recalibration is recommended at least every 12 months.
Max/Min Display: Stored until reset by user or meter is turned off.
Password: Restricts modification of programmed settings.
Non-Volatile Memory: Settings stored for a minimum of 10 years.
Power: 85-265 VAC, 50/60 Hz; 90-265 VDC, 20 W max
Required Fuse: UL Recognized, 5 A max, slow-blow; up to 6 meters may share one fuse.
Normal Mode Rejection: 64 dB at 50/60 Hz
Isolation: 4 kV input/output-to-power line; 500 V input-to-output or output-to-24 VDC supplies.
   -6R5 & -6X5 models only: 100 V output-to-24 VDC supply
Operating Temperature: -40 to 65°C
Storage Temperature: -40 to 85°C
Relative Humidity: 0 to 90% non-condensing
    Power & Signal: removable screw terminal blocks accept 12 to 22 AWG.
    Serial: RJ11 header, standard on all meters.
Enclosure: 1/8 DIN, high impact plastic, 94V-0, color; gray
Weight: 9.5 oz (269 g) (including options)
UL File Number: E160849; 508 Industrial Control Equipment
Warranty: 3 years parts & labor

Process Inputs

Inputs: Field selectable: 0-20 mA, 4-20 mA, 1-5 V, ±10 V
Accuracy: ±0.05% FS ±1 count; square root: ±0.1% FS ±2 counts
Function: Linear or square root
Low-Flow Cutoff: 0 to 9999 (0 disables cutoff function)
Decimal Point: Up to 3 decimals: d.ddd, dd.dd, ddd.d, or dddd
Calibration: Scale without signal or calibrate with signal source
Calibration Range: User programmable over entire range of meter
Input Impedance: Voltage range: greater than 1 M Ω, Current Range: 50-100 Ω, varies with resettable fuse impedance
Input Overload: Protected by automatically resettable fuse
Temperature Drift:
0 to 65°C ambient-40 to 0°C ambient
Current: ±0.20% FS (50 PPM/°C)Current: ±0.80% FS
Voltage: ±0.02% FS (1.7 PPM/°C)Voltage: ±0.06% FS

Transmitter Supply: Isolated, one or two transmitter supplies
  P1: 24 VDC ±10% @ 200 mA max (-1 option)
  P1 & P2: 24 VDC ±10% @ 200 mA & 40 mA max (-2 option)

Temperature Inputs

Inputs: Factory calibrated, field selectable: type J, K, T, or E thermocouples and 100 Ω platinum RTD (0.00385 or 0.00392 curve)
Resolution: 1°; type T: 1° or 0.1°
Cold Junction Reference: Automatic
Temperature Drift: ±2°C maximum
Offset Adjustment: Programmable to ±19.9°. This parameter allows the user to apply an offset value to the temperature being displayed.
Input Impedance: Greater than 100 k Ω
Sensor Break: All relays and alarm status LEDs go to alarm state.

Input TypeRangeAccuracy
(0-65° C)
(-40-0° C)
Type J-58° to 1382° F
-50° to 750° C
±2° F
±1° C
±5° F
±3° C
Type K-58° to 2300° F
-50° to 1260° C
±2° F
±1° C
±4° F
±2° C
Type T-292° to 700° F
-180° to 371° C
±2° F
±1° C
±13° F
±7° C
Type T
0.1° Res
-199.9° to 700.0° F
-180.0° to 371.0° C
±1.8° F
±1° C
±13° F
±7.2° C
Type E-58° to 1578° F
-50° to 870° C
±2° F
±1° C
±11° F
±6° C
100 Ω RTD-328° to 1382° F
-200° to 750° C
±1° C
±3° C


Rating: 2 Form C (SPDT); rated 3 A @ 30 VDC or 3 A @ 250 VAC resistive load; 1/14 HP @ 125/250 VAC inductive loads
Deadband: 0-100% FS, user selectable
High or Low Alarm: User may program any alarm for high or low
Relay Operation:
  1. Automatic (non-latching)
  2. Latching
  3. Pump alternation control
Relay Reset: User selectable via front panel buttons or PC
  1. Automatic reset only (non-latching)
  2. Automatic plus manual reset at any time (non-latching)
  3. Manual reset only, at any time (latching)
  4. Manual reset only after alarm condition has cleared (latching).
Automatic Reset: Relays reset when input passes the reset point
Manual Reset: Front panel button, MeterView, Modbus registers
Time Delay: 0 to 199 seconds, on and off delays; programmable
Fail-Safe Operation: Programmable, independent for each relay. Relay coils are energized in non-alarm condition. In case of power failure; relays will go to alarm state.
Auto Initialization: When power is applied to the meter, relays will reflect the state of the input to the meter.

Isolated 4-20 mA Transmitter Output

Scaling Range: 1.00 to 23.00 mA; reverse scaling allowed.
Calibration: Factory calibrated 4.00 to 20.00 mA
Accuracy: ±0.1% FS ±0.004 mA
Temperature Drift: 50 PPM/°C
Note: Analog output drift is separate from input drift
Isolation: 500 V input-to-output or output-to-24 VDC supplies; 4 kV output-to-power line
External Power: 35 VDC maximum
Output Loop Resistance:
Loop Resistance
Power SupplyMinimumMaximum
24 VDC10 Ω700 Ω
35 VDC (external)100 Ω1200 Ω

Serial Communications

Compatibility: EIA-232, EIA-422, and EIA-485 with PDA7232 and PDA7422 Trident adapters.
Protocol: Two selectable. PDC protocol (for use with MeterView) and Modbus RTU
Meter Address: PDC protocol: 0 to 99, Modbus protocol: 1 to 247
Baud Rate: 300 to 19,200 bps
Transmit Time Delay: Programmable 0 to 199 ms or transmitter always on for RS-422 communications.
Data: 8 bit (1 start bit, 1 stop bit)
Parity: None (2 stop bits), even, or odd
(Modbus only; PDC protocol does not use parity)
Byte-to-Byte Timeout: 0.01 to 2.54 seconds (Modbus only)
Turn Around Delay: Less than 2 ms (fixed)
Refer to PDC and Modbus Serial Communications Protocol manuals for details.
Note: Both downloadable protocol register tables can be found in the documentation list below.

PD138 Scanner

Number Of Channels: 8 double-pole channels per unit
Number Of Channels Per System: Unlimited
Signals Switching: DPST reed relays
Contact Resistance: 0.2 Ω maximum
Maximum Input Voltage: 200 V (switched or common mode)
Maximum Current Switched: 0.5 A
Maximum Power Switched: 10 W
Dwell Time: Each channel adjustable from 0.6 to 30 seconds
Non-Volatile Memory: All programming values are stored in non-volatile memory for ten years if power is lost
Scan Method: Internal or manually controlled
Channel Indication: Green LED on front panel
Disabling Channels: Any channel may be disabled during setup
Scan Stop: The scan may be stopped by pressing and holding the STOP/GO button for more than 0.5 seconds. The scan may be resumed by pressing and releasing the STOP/GO button quickly (less than 0.5 seconds)
Alarm Input: Independent alarm input for each channel. Input Impedance; 25 K Ω, typical pull-up to 5 V
Alarm Sequence: Sequence A or Sequence F2A (first out)
Alarm Outputs: Alarm condition indicated by:
  1. Front panel red LED for each channel
  2. Relay, 1 SPDT (form C); rated 2 Amp @ 30 VDC or 2 Amp 2. @ 250 VAC resistive load; 1/14 HP @ 125 /250 VAC for inductive loads. For fail-safe operation, the relay is energized in the non-alarm state. In the case of a power failure, the relay will go to the alarm state, (NC contact is connected to common)
  3. Built-in Horn, 85 dB
  4. Stop-on-alarmed-channel (user select)
Alarm Acknowledge: Front panel ACK and rear connector terminals
External Switch Functions: The functions of the front panel buttons are available at screw terminals at the rear of the instrument
Message Labels: Free, custom printed, 2 lines per message at 14 characters per line. Factory or field printable. See manual for details
Connections: Removable screw terminal connectors provided:
Power + Relay: 22 to 12 AWG; Alarm Input, Analog Signal, External Switches, I/O: 30 to 16 AWG
Operating Temperature: -40°C to 65°C
Storage Temperature: -40°C to 85°C
Relative Humidity: 0 to 95% non-condensing
Power: 115 VAC, ±10%, 50/60 Hz, 22 W max
Led Test: All LEDs are tested on power-up
Enclosure: 1/8 DIN, high impact plastic, UL94V-0
Front Panel: NEMA 4X, panel gasket provided
Warranty: 3 years parts & labor

PDA2821 Enclosure

Dimensions: 11" x 7.5" x 7.1" (190mm x 280mm x 180mm)
Material: Plastic
Color: Gray
Ratings: NEMA 4X (PDA2801: NEMA 4)

Note: This tab applies to the entire product series and may contain information that is not relevant to this particular model number.

MeterView for Trident

Meterview for PD765 or PD8-765

Note: PD765 is not powered from USB connection and requires external power to be programmed.

MeterView software allows remote programming and data acquisition of the Trident series. The remote programming allows for all available meter settings to be programmed from a personal computer through an easy user-friendly interface. The data acquisition allows the user to gather readings from up to 100 meters at user-selected intervals and generate charts using common tools like Microsoft Excel.

Click here for more information about MeterView software.
Click here for a short video on the hardware requirements for MeterView.

Digital Panel Meters make a great front end to a PC-based data acquisition system. They are easy to set up, can be used for a wide range of inputs, will power the transmitter, and best of all provide a local display of the process. Precision Digital has the perfect package with its Trident Digital Panel Meters, a wide selection of serial adapters and converters and free MeterView software. Data is displayed on the PC and written to a file that could then be imported into a spreadsheet or other application.

Data Logging up to 100 Trident Meters

Sample File Generated by MeterView

Great for tank level monitoring!

Ordering Example: System consisting of 10 Tridents & MeterView

10PD765-6R2-10Trident with 2 Relays & 24 VDC Transmitter Supply
10PDA7422Trident RS-485 Serial Adapter
1PDA8485-IUSB to RS-422/485 Isolated Converter
1PDA7503-2MeterView Software for 1-10 Meters


PD138 and PD765 to Scan Thermocouples

In the following application example, four oven thermocouples are scanned and channeled to a PD765 Temperature Meter where the PV is displayed and checked for low or high alarm conditions. All four ovens share the same low and high alarms, so the alarm inputs are joined together on the PD138.
The PD138 MINIMUX® II is programmed in the following manner to satisfy this application:

  • Select alarm Sequence A
  • Stop-on-alarm is off
  • Program dwell times:
    • Channel 1 for ten seconds
    • Channel 2 for five seconds
    • Channel 3 for fifteen seconds
    • Channel 4 for five seconds
    • Channels 5-8 are disabled

The PD765-6R2-00 Trident is programmed in the following manner to satisfy this level application:

  • Select T/C
  • Select °F
  • Program alarm set and reset points:

The MINIMUX II scans each input and reflects the alarm state. The PD138 shown above is scanning input 1 (Green LED) allowing the Trident to display the current temperature of 250°. No alarm is present since the temperature is within limits. The MINIMUX® II only responds to new alarm conditions detected in the currently active channel. The PD138 also avoids false alarms by detecting alarm conditions only after dwelling on a channel for 2 seconds, or 0.05 seconds before it has been programmed to go onto the next channel if the dwell time had been programmed for less than 2 seconds. This gives the PD765 time to stabilize and accurately display the temperature and to check for alarm conditions.

The MINIMUX II switches to (scans) input 2 channeling it to the PD765-6R2-00 where a temperature of 345° is found to cause a high alarm condition. The PD138 is programmed for Sequence A, so the channel 2 LED alternately flashes yellow and green, the internal horn sounds, and the PD138's alarm relay transfers causing an external horn to sound. After acknowledging the alarm the channel LED will glow a steady yellow (while selected), or steady red (when not selected) until reset.

The MINIMUX II switches to (scans) input 2 channeling it to the PD765-6R2-00 where a temperature of 345° is found to cause a high alarm condition. The PD138 is programmed for Sequence A, so the channel 2 LED alternately flashes yellow and green, the internal horn sounds, and the PD138's alarm relay transfers causing an external horn to sound. After acknowledging the alarm the channel LED will glow a steady yellow (while selected), or steady red (when not selected) until reset.

The MINIMUX® II switches to (scans) input 3 channeling it to the PD765-6R2-00 where a temperature of 220° is found to cause a low alarm condition 2 seconds into the dwell time. Channel 3 LED alternately flashes yellow and green (shown yellow), the internal horn sounds and the PD138's alarm relay transfers causing an external horn to sound.


Mounting Dimensions

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Stock: 2
Lead Time: 6 business days