Pods - PD4


The "PD4 System" was designed specifically as an Entry Level SCADA System. Made up of any number of PD4 units (monitoring inputs from your production processes, plant or simple status inputs) communicating over air using mobile phone technology to a central PC used to display incoming alarms and status changes as well as for archiving and exporting data. Alternatively, PD4's can report status as SMS text messages directly to mobile phones or pagers.

The schematic below shows how the elements of the PD4 System fit together


One of the core objectives in designing the PD4 System was to allow customers to install, commission and maintain their own
entry level SCADA system without the need for expensive equipment, specialist knowledge or expensive training. A truly entry
level system would need to be 'delivered in a box' with 'how to' documentation.


The PD4 Remote Site Monitor is the "sharp end" of the system. Each PD4 unit monitors the status of equipment and "reports by
exception" user defined alarm conditions to the Host Terminal via the GSM network. Output contacts in the PD4 unit allow remote
control of plant from the Host Terminal. The built in sealed lead acid battery and charger allow continuous operation during power supply interruptions.

Suitable applications could be the monitoring of any site where equipment status needs to be monitored, examples include:

  • Circuit Breakers in HV/MV substations
  • AC supplies to pumps, fans and motors
  • Door or gate positions
  • Pressure, temperature, humidity sensors
  • Any other remote/unmanned equipment

When fitted with output relay contacts, the Host Terminal operator can send control commands to the PD4 to operate remote
equipment such as fans, power supplies, lighting or circuit breakers etc.

PD4 Features:

  • Wall mounting IP54 polycarbonate casing
  • LCD display
  • Test buttons 
  • I/O
  • 3 x 240Vac or 110Vac monitoring
  • 8 digital inputs, software configurable as NO/NC and pulse/latching
  • 4 analogue inputs, 8 bit resolution, configurable high and low alarm thresholds
  • 3 relay outputs, steady state or pulsed


  • 900 GSM modem with antenna, 1800 and 1900 frequency options
  • Alternative option for PSTN (telephone land line)
  • Alternative option for PAKNET radio 
  • Protocol options include DNPS or proprietary

Power Supply

  • Auxiliary AC supply charges 6V Cyclon lead acid battery - gives 8 hours standby
  • Low battery volts alarm call function
  • Alternative for 24V dc (replaces the battery)


The PD4 unit uses a GSM modem to communicate with the Host Terminal. The GSM network provides links to standard land line
networks (just as you can make a voice call from your office to your cell phone and vice versa). The Host Terminal can have a standard PSTN land line modem and connection.

Conventional approaches to SCADA would typically use leased lines, point-to-point radio or trunked radio solutions. GSM is far easier to use and maintain as well as being much lower in cost than any of these systems.

GSM networks are already widely available across all continents and in most countries. Often there is a choice of GSM provider and, with the competition for voice users, the coverage and cost of use of GSM is making the technology more and more appealing. Conventional GSM data speeds of 9600baud mean that a PD4 transfers data to the Host Terminal in a matter of a few seconds.

You can configure the PD4 unit to send alarms to mobile phones as SMS Text Messages as well as to the Host Terminal. The
standard PD4 is supplied with a GSM modem built in. In order for the PD4 to work correctly all you need to confirm is:

Is there GSM coverage (there may be coverage from more than one GSM Network)?
Is "data" service available on the GSM Network?
If more than one possible network provider, which offers the best signal strength/cost of use?
Which frequency does the network operate on (900/1800/1900 MHz)?

To allow the PD4 access to the GSM Network, the GSM modem in the PD4 must be fitted with a SIM card. This SIM card is issued and then "activated" by the GSM Network provider. The SIM card is not supplied as part of the PD4 unit.

Host Terminal

The PD4 Host Terminal is the focal point of the PD4 system. It is simple to install and use, with a variety of useful features to
enable quick response to alarm conditions detected at remote sites. The specification is as follows:
  • Pentium PC running Windows 95/98/NT/XP/2000  
  • The PD4 Host Application software (from NHDS)
  • GSM modem(s) and/or PSTN (telephone line) modem(s)

The Host Application is a bespoke software program written in C++ which provides the user friendly intuitive MMI for the PD4
System. The Host Application offers the following main facilities:

  • Alarm Screen listing sites with current alarms
  • Site Display showing the status of equipment monitored by individual PD4 units
  • Archived alarms and event data with a variety of on screen search criteria
  • Answers incoming calls from PD4 units and updates displays and logs data
  • Polls PD4 sites to request status
  • Reprogram operational settings
  • Can simultaneously communicate with up to 16 remote PD4 units
  • Stores database records for PD4 site locations and operational settings
  • Flexibility to customise the alarms screens and database fields
  • Host Terminal Operational Status screen
  • Export data to other file formats
  • Can forward alarms/status messages directly to mobile phones/pagers as SMS text messages

We provide a "Training Version" of the Host Application to allow users to familiarise themselves with the system. You can simulate incoming alarms, create new remote sites, reprogram operational settings, export data - in short, all the functions of a live system but in a dummy environment.

DNP3 Communications Protocol. In order to maintain upward compatibility with "HIGH END" SCADA systems, NHDS can provide a DNP3 compliant version of the PD4, thus allowing integration into standard SCADA system.

Click here to view the following PDF  :: PD4 Fact Sheet
We also have the following available ::  PD4 Configuration Kit    PD4 Training