Temperature Measurement · Thermocouples
Spring-clamp thermocouple with a stainless steel M12×1.5 threaded head and a braided high-temperature shielded lead, for moulds, extruders, heating bands and other points that need a probe pressed into place.
A clamp-on thermocouple measures the temperature of a machine surface or a drilled point by holding a spring-loaded probe against it. The measuring junction sits inside a small stainless steel tip, and the body that carries it is a rotating clamp with an extended spring, so the insertion depth can be set at the point of measurement rather than being fixed by the length of the probe. On injection moulding machines, extruders, moulds and heating bands, that is usually the practical difference: the probe has to be pressed into a nozzle, a barrel or a band in a place with no room for a threaded assembly and no access for a spanner.
The build on this page is type K as standard, with type E and a PT100 resistance element offered in the same body. Type K covers 0 to 800°C, type E 0 to 400°C and the PT100 -200 to 450°C. The threaded head is stainless steel M12×1.5 and unscrews, leaving a plain clamp-on probe where there is no threaded boss to use. The lead is a braided stainless steel sheath over a shielded high-temperature cable, in lengths from 1 to 5 m, and the tip material is iron.
The junction is welded rather than twisted. The supplied material makes a point of this: the two conductors are joined inside the tip by argon arc welding and insulated with a high-frequency ceramic tube, which is a different construction from the common practice of twisting the conductors together, and it is the difference that shows up as stability at the top of the range.
A thermocouple produces a voltage rather than a resistance. Two dissimilar metals joined at one point generate a small potential difference when that junction sits at a different temperature from the other end of the wires, and the voltage is a few tens of microvolts per degree. Nothing has to be supplied to the sensor for it to work, which is why a thermocouple suits the top of the temperature range where a resistance element would drift, and why it can be made very small.
That same principle sets the constraints. Because the voltage is generated between the measuring junction and the terminals where the wires land, the temperature at those terminals is part of the measurement: the instrument has to know the terminal temperature and compensate for it. It also means the circuit has to be made up with the matching thermocouple wire throughout. Every place where the thermocouple wire meets a copper conductor is itself a thermocouple junction, and one that is not at the terminal temperature contributes an error rather than a connection.
The two junction forms in the supplied material follow from how the tip is built. In a grounded junction, the welded joint is also in electrical contact with the sheath, so heat reaches it quickly and the response is fast, but the measuring circuit is connected to whatever the sheath touches. In an ungrounded junction, the joint sits insulated inside the tip, which isolates the circuit at the cost of a slower response. The material offers both and states no response time for either, so the choice is on the grounds of the installation rather than a published figure.
Two further practical properties come from the construction. The braided sheath over the cable is a mechanical protector and a shield at the same time, which matters on a machine carrying drives and heaters where an unshielded millivolt signal picks up interference. And the sheath is stainless steel while the tip is iron, so the probe tolerates contact with the machine without the lead becoming stiff and brittle the way a plain polymer cable would near a hot band.
Start with the temperature and the instrument. The calibration type follows the range: type K to 800°C, type E to 400°C, or the PT100 variant where a resistance element suits the instrument better. From there the decision is forced, because the sensor has to match the input type of the temperature instrument it connects to. A PT100 on a type K input gives a plausible and wrong display, and the supplied material flags exactly that.
Then the mounting. Where the machine has a threaded boss at the measuring point, the stainless steel M12×1.5 head screws into it and the spring sets the contact pressure. Where it does not, the head is unscrewed and the probe is clamped directly. The clamp seat is 11.5 mm inside and 13 mm outside with an 18 mm height, and 12 mm and 14 mm versions are available to order, so the seat has to match the boss or hole it sits in.
Then the junction form, grounded or ungrounded, for the reasons above: speed against isolation.
Then the lead. The standard range is 1 to 5 m with 1 m, 5 m and 7 m named as the usual lengths, and other lengths to order. A run longer than the standard range means an extension, and an extension has to be made of the same thermocouple wire with matching connectors; the supplied material does not specify those. Where the lead passes near a hot surface, or along a moving axis, the braided sheath is what protects it, and the minimum bend radius for that is not stated.
Finally the termination. Fork terminals are standard with red to positive and blue to negative. Where the instrument terminal does not accept a fork, pin terminals can be made to order.
The sensor is not a traceable measuring instrument on its own. The supplied material gives no accuracy class or tolerance for the thermocouple, and no response time, so this page states the ranges but not a measurement uncertainty. Where a reading has to be defended, the thermocouple needs to be paired with a transmitter or instrument whose accuracy is known and, ideally, verified against a reference.
The lead is a limit that is easy to overlook. A probe rated to 800°C at the tip does not mean the lead survives 800°C, and the supplied material does not state the temperature rating of the cable or its insulation. The measuring point and the route the lead takes therefore need to be considered separately.
Several properties named in the material are not quantified. The probe is described as able to bend and to withstand high pressure, but no minimum bend radius and no pressure figure are given, so neither is published here. The material also gives a standard lead range of 1 to 5 m and then includes 7 m among the usual lengths, which is outside that range as stated.
Finally the identification is open. The supplied material gives the calibration type under the model field rather than a part number, and a calibration type is common to every supplier of that thermocouple, so it is not used here as an identifier. An order should state the calibration type, the junction form, the lead length, the termination and the clamp seat dimensions.
Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.
| Calibration types | K type as the standard build; E type and PT100 offered in the same bodyStandard |
|---|---|
| Measuring range, K | 0 to 800°CStandard |
| Measuring range, E | 0 to 400°CStandard |
| Measuring range, PT100 | -200 to 450°CStandard |
| Junction form | Grounded and ungrounded versions are both offeredStandard |
| Junction construction | The two conductors are welded together inside the tip by argon arc welding and insulated with a high-frequency ceramic tube, as distinct from conductors that are merely twisted togetherStandard |
| Accuracy class or tolerance | Information requiredInformation required |
| Response time | Information requiredInformation required |
| Reference standard for the thermocouple output | Information requiredInformation required |
| Probe front | 5 mm outside diameter tube, 10 mm protrudingStandard |
|---|---|
| Spring section | 21 mm; the rotating clamp head allows the insertion depth to be set on siteStandard |
| Clamp seat | 11.5 mm inside and 13 mm outside as standard; 12 mm and 14 mm to orderStandard |
| Clamp seat height | 18 mmStandard |
| Threaded head | 12 mm diameter × 34 mm, M12×1.5 threadStandard |
| Threaded head removal | The threaded head can be unscrewed, leaving the plain clamp-on formStandard |
| Tip material | IronStandard |
| Thread, braid and spring material | Stainless steelStandard |
| Clamp tube supplied as standard | Φ5×21 mm with the PT100 buildStandard |
| Ingress protection | Information requiredInformation required |
| Maximum pressure at the probe | Information requiredInformation required |
| Weight | Information requiredInformation required |
| Lead length | 1 to 5 m in the standard range, with 1 m, 5 m and 7 m given as usual lengths; other lengths to orderStandard |
|---|---|
| Lead construction | Braided stainless steel wire over a shielded high-temperature cableStandard |
| Conductor count | Two for K and E; PT100 is three-wire as standard, and can be made two-wire or four-wireStandard |
| Standard termination | Fork terminals; red to positive, blue to negativeStandard |
| Alternative termination | Pin terminals to orderOptional |
| Lead temperature rating | Information requiredInformation required |
| Minimum bend radius | Information requiredInformation required |
| Instrument matching | The sensor and the temperature instrument must share the same input type. A PT100 input requires a PT100 sensor and a type K input requires a type K sensorStandard |
|---|---|
| Extension compensation | Not stated in the supplied materialInformation required |
| Polarity convention | Fork terminals are colour coded red to positive and blue to negativeStandard |
| Warranty | Information requiredInformation required |
|---|---|
| Certification | Information requiredInformation required |
| Test or conformity certificate | Information requiredInformation required |
| Datasheet | Information requiredInformation required |
| Packaging quantity and gross weight | Information requiredInformation required |
| Model | Configuration | Key ranges | Availability |
|---|---|---|---|
| K type | Two conductors, 0 to 800°C, M12×1.5 threaded head | 0 to 800°C | Standard build; the only calibration type in the supplied material with a stated range above 450°C |
| E type | Two conductors, 0 to 400°C, M12×1.5 threaded head | 0 to 400°C | |
| PT100 | Three conductors as standard, two or four to order | -200 to 450°C | Resistance element rather than a thermocouple, so it needs a PT100 input |
| Plain clamp-on | Threaded head removed, spring clamp only | Per the calibration type ordered | The threaded head unscrews, so this is a configuration rather than a separate part |
| Custom lead and termination | Lead length outside 1 to 5 m, pin terminals | Per the calibration type ordered | Made to order |
Certifications are only published once a certificate copy can be produced, so this section is deliberately empty rather than populated with assumed approvals. Tell us which approvals your application requires and we will confirm what is available for this instrument.
The following are required for a complete specification but are not stated in the documentation supplied to us. They are listed rather than estimated:
They measure temperature by different effects. A K type thermocouple generates a small voltage at a junction of two dissimilar metals and uses two conductors; a PT100 is a resistance element and uses three conductors as standard so that the lead resistance cancels. The supplied material states the two cannot be mixed: a sensor must match the input type of the instrument it is connected to, so a PT100 probe on a type K input will not display the correct temperature.
Through the spring clamp. The clamp head rotates and the spring is extended, so the probe can be pressed into a drilled hole or set against a surface and the insertion depth adjusted on site. Where the point has a threaded boss, the stainless steel M12×1.5 head can be screwed in; where it does not, the head unscrews and the probe is used as a plain clamp-on.
Two reasons, both stated in the supplied material. The braid protects the conductors mechanically on a machine that moves and vibrates, and the shielding protects the thermocouple signal, which is only a few tens of millivolts, from electrical interference on a machine with drives and heaters nearby. The braid also allows the lead to be bent to follow a machine contour.
Both are offered and the choice depends on the measuring point. A grounded junction gives a faster response because the tip is in direct thermal and electrical contact with the sheath, but it creates an electrical path between the measuring circuit and whatever the sheath touches. An ungrounded junction isolates the circuit and is the usual choice where the probe is fixed to earthed metal or where a stray current path would disturb the reading. The supplied material does not state a response time for either form.
The material gives 1 to 5 m as the standard range, with 1 m, 5 m and 7 m as the usual lengths, and other lengths to order. Because a thermocouple circuit must be made up with the correct thermocouple wire rather than with copper, a long run needs the matching extension wire and connector, and neither is specified in the supplied material.
The measuring range is a property of the calibration type: 0 to 800°C for K, 0 to 400°C for E and -200 to 450°C for PT100. The lead is a separate limit, and the supplied material does not state the temperature rating of the cable or of the insulation, so a point that runs near the top of the range should have that confirmed before the probe is installed.
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