Browse Temperature Instruments
Electronic temperature sensors
Electronic sensors convert temperature into an electrical signal for display, control and data logging. They’re usually paired with a temperature transmitter or signal conditioner.
Thermocouples
Suitable for: Liquids · Gases · Steam (in a thermowell) · Solids (surface probes)
A thermocouple is made of two wires of different metals joined at one end, the measuring junction. When that junction is at a different temperature from the other end of the wires, a small voltage, called the electromotive force (EMF), is produced. The voltage rises with temperature, though not in a straight line, so the instrument linearises it. Because the voltage depends on the temperature difference, the instrument also measures the temperature at the connection point and compensates for it, a process called cold junction compensation.
Thermocouples are rugged, respond quickly and cover a very wide temperature range, including the high temperatures found in furnaces, kilns and exhausts.
Resistance temperature detectors (RTDs)
Suitable for: Liquids · Gases · Steam (in a thermowell) · Solids (surface probes)
Resistance temperature detectors (RTDs) work on the principle that a metal’s electrical resistance changes with temperature. The most common types, Pt100 and Pt1000, use platinum, with a resistance of 100 Ω or 1000 Ω at 0 °C that rises almost linearly as temperature increases. RTDs offer high accuracy, stability and repeatability, which makes them the usual choice for process and laboratory measurement at moderate temperatures.
Thermistors
Suitable for: Liquids · Gases · Solids (surface probes)
Thermistors use a ceramic semiconductor whose resistance changes sharply, and non-linearly, with temperature. They’re very sensitive over a narrow range, so they’re widely used in HVAC, refrigeration, appliances and equipment protection.
Infrared thermometers
Suitable for: Liquids (surface only) · Solids (surfaces)
Infrared thermometers measure temperature without contact, by detecting the thermal radiation a surface gives off and focusing it onto a sensing element. They’re ideal for moving, hot, hard-to-reach or hazardous surfaces. Accuracy depends on setting the right emissivity for the surface, and on the distance to the target relative to the measured spot size.
Custom probes and temperature transmitters
We make custom RTD and thermocouple temperature probes to your specification. Temperature transmitters convert the sensor’s signal into a standard output, such as 4–20 mA or a digital protocol, so it can travel reliably to your control or data logging system.
Mechanical thermometers
Mechanical thermometers need no power and give a direct local reading. They work because materials expand as they heat up.
Bimetal temperature gauges
Suitable for: Liquids · Gases · Steam (in a thermowell)
A bimetal temperature gauge uses two strips of different metals bonded together, usually wound into a coil. The metals expand at different rates, so the strip bends or twists as the temperature changes. That movement turns the pointer, or operates a set of switch contacts. Teltherm is the only New Zealand manufacturer of bimetal analogue temperature gauges.
Gas- and liquid-filled thermometers
Suitable for: Liquids · Gases · Steam (in a thermowell)
Filled thermometers use the expansion of a fluid sealed in a bulb. As the temperature changes, the fluid, usually an inert gas or a liquid, expands or contracts, and the change in pressure or volume moves the pointer. A capillary can link the bulb to a dial some distance away. Mercury has largely been phased out because it’s an environmental hazard, and its use is restricted.
Humidity measurement
Humidity is the amount of water vapour in the air. Humidity and temperature are often measured together, in HVAC, food processing, agriculture, museums and manufacturing, to keep environments stable and protect products.
Humidity measurements explained
Suitable for: Gases (air and process gases)
• Relative humidity (RH) is the amount of water vapour in the air as a percentage of the most the air could hold at that temperature. It’s the most common humidity measurement.
• Absolute humidity is the mass of water vapour in a given volume of air, such as grams per cubic metre.
• Specific humidity is the mass of water vapour per mass of moist air.
• Dew point is the temperature at which the water vapour would start to condense. It’s widely used for compressed air and drying processes.
Humidity instruments
Suitable for: Gases (air and process gases)
Most humidity instruments use a capacitive polymer sensor, which absorbs water vapour and changes its capacitance in proportion to relative humidity. Humidity transmitters, probes and handheld meters are available on their own or combined with temperature measurement. We supply humidity instruments from a specialist manufacturer and will help you choose the right one.
Choosing the right temperature instrument
To recommend the most accurate and suitable instrument for your process, we discuss:
• the accuracy and temperature range you need
• the process itself: pressure, media, speed of response and connections
• the electrical output signals you need
• environmental conditions, both inside the process and around it
• maintenance requirements.
Which technology suits your application?
| Technology | Liquids | Gases | Steam | Solids (surfaces) | Best for |
|---|---|---|---|---|---|
| Thermocouple | ✓ | ✓ | ✓ (thermowell) | ✓ | Wide range, high temperatures |
| RTD (Pt100/Pt1000) | ✓ | ✓ | ✓ (thermowell) | ✓ | High accuracy and stability |
| Thermistor | ✓ | ✓ | – | ✓ | Sensitive, narrow range |
| Infrared | Surface only | – | – | ✓ | Non-contact measurement |
| Bimetal gauge | ✓ | ✓ | ✓ (thermowell) | – | Local display, no power |
| Gas- or liquid-filled | ✓ | ✓ | ✓ (thermowell) | – | Local or remote dial |
| Humidity instrument | – | ✓ (air) | – | – | Relative humidity, dew point |
Calibration and service
Our temperature, infrared temperature and humidity calibration is accredited by IANZ to ISO/IEC 17025, and we also maintain and repair temperature and humidity instruments. Temperature calibration can be done in our laboratory or on your site; infrared and humidity calibration is done in our laboratory. See Instrument Calibration NZ for more.
Frequently asked questions (optional)
Should I use a thermocouple or an RTD?
Choose an RTD when you need high accuracy and stability at moderate temperatures. Choose a thermocouple for very high temperatures, a fast response or a rugged, low-cost sensor.
What is a Pt100?
A Pt100 is a platinum resistance temperature detector with a resistance of 100 Ω at 0 °C. Its resistance rises almost linearly with temperature, which makes it accurate and easy to use. A Pt1000 works the same way, with 1000 Ω at 0 °C.
Are your temperature gauges made in New Zealand?
Yes. Teltherm is the only New Zealand manufacturer of bimetal analogue temperature gauges, and we also make custom RTD and thermocouple probes to your specification.
What’s the difference between relative humidity and dew point?
Relative humidity is the water vapour in the air as a percentage of the maximum it could hold at that temperature, so it changes as the air warms or cools. Dew point is the temperature at which that vapour would condense, and it stays the same as the air warms or cools, as long as no moisture is added or removed.
How often should temperature and humidity instruments be calibrated?
As a general guide, working temperature instruments every 12 months, with an ice point check every 3–6 months, and humidity and infrared instruments every 12 months. Reference thermometers can go 5 years if ice point checks are done every 6–12 months.