OxyGuard Handy Polaris TGP

Handy Polaris TGP - 3 Meters in 1

The OxyGuard Handy Polaris TGP is a hand-held gas pressure meter. It can operate in three modes, one where it acts as a standard Polaris dissolved oxygen meter, one where it is a Total Gas Pressure meter that shows pressures as “percent saturation” values of the actual atmospheric pressure and one where it is a Total Gas Pressure meter that shows pressures as volume percentages.

To do this it measures the atmospheric pressure, the total dissolved gas pressure, the oxygen partial pressure and the temperature.

The instrument incorporates a data logger. Messages on the display, and menu functions, make the Handy TGP easy to use

TGP Probe

The OxyGuard TGP probe measures Total dissolved Gas Pressure and is designed specifically for use with OxyGuard Commander, Convoy or Pacific systems. It can be added to existing systems. It contains sensors for dissolved gas pressure, static (water) pressure and temperature.

When placed in water that is completely saturated with air and in equilibrium with (moist) air at the standard atmospheric pressure of 1013.25 millibar the OxyGuard TGP will measure this gas pressure, which is made up of the following partial pressures at 20°C:

  • Oxygen: 207.32 millibar
  • Other gases, e.g. nitrogen and argon: 782.08 millibar
  • CO2: 0.4 millibar
  • Water vapour: 23.46 millibar

The OxyGuard TGP is used to show if the water is super-saturated with “other gases”. Measurements of dissolved oxygen and atmospheric pressure made in the system that the TGP is used with enable the “other gas” partial pressure to be calculated. The partial pressure of dissolved CO2 can also be taken into consideration, for example if an OxyGuard CO2 measurement is included in the system.

Technical Advantages


The Polaris 2 TGP is designed for easy use and to give accurate here-and-now measurements of both the dissolved oxygen and the dissolved rest gases - i.e. the gases that can cause decompression sickness - “the bends” - in fish. This is achieved because the instrument measures all three pressures needed - the dissolved oxygen, the total dissolved gas and the atmospheric.

Maintenance is easy - the DO measurement is made using the well-known OxyGuard Handy probe, and the TGP measurement tube sensor element can easily be exchanged if necessary.


The OxyGuard TGP probe can be directly connected to OxyGuard Commander, Convoy and Pacific systems. It can only be used with these systems. It does not need a separate transmitter or input unit, but communicates values directly. Only one field bus data cable connection is needed - the cable has cores for both data and the 24 V DC supply needed by the probe.

The TGP is designed for easy use. The measurement tube is wound on a central bobbin that is held in place by the protector. If the tube becomes fouled you simply unscrew the protector, unplug the bobbin and tube and fit a replacement.

Precise measurements are obtained by placing the TGP in the air and matching - or calibrating - the TGP against the barometric pressure sensor of the DO Meter or Pacific of the system. This means that a very accurate value of the difference between the gas pressure in the water and the gas pressure in the air can be obtained. The pressure measurements can also both be calibrated against the absolute value of the barometric pressure if this is known accurately.

The TGP has the same diameter as a standard OxyGuard probe so that standard mounting devices can be used.