JUMO 909740 Replacement Measuring Inserts for Screw-In RTD Probes and Thermocouples

Replacement measuring inserts for form B screw-in probes

The JUMO 909740 data sheet covers exchangeable measuring inserts for screw-in thermocouples and screw-in resistance thermometers with terminal head form B, for temperatures from -200 to +1150 degC. They are supplied as single or twin inserts and can be fitted with a transmitter in place of the terminal block. JUMO states that the inserts suit screw-in thermocouples to data sheet 90.1020 and screw-in resistance thermometers to data sheets 90.2020 and 90.2820. A mineral-insulated insert has to be used for insert lengths from 800 mm.

Resistance-thermometer inserts (909740) are normally fitted with a Pt100 to EN 60751 class B in 2-wire circuit, with Pt500 or Pt1000 available and a choice of 3-wire or 4-wire connection. Thermocouple inserts (909742) use Fe-Con L or NiCr-Ni K elements. The terminal block is suitable for terminal heads form B, BBK and BUZ. Replacing an insert restores a drifting or broken sensor without taking the thermowell or sheath out of the process.

Technical specifications

Matching an insert to the probe it replaces

Insert length is the critical match. The datasheet lists standard pairings for resistance thermometers 902020/10: an insert of 315 mm for a probe with fitting length 160 mm, 405 mm for 250 mm and 555 mm for 400 mm. Other lengths are given in plain text. Diameter is 3 or 6 mm and must fit the bore of the existing protection tube. The order code for RTD inserts is basic version – operating temperature – measuring insert – tolerance class – diameter – length / extra codes, for example 909740/10 – 402 – 1003 – 1 – 6 – 315 / 000.

For thermocouple inserts use basic version 909742/30 (rigid insert) or 909742/40 (mineral-insulated), choose the temperature code 150, 165 or 182, then the element and diameter. Specify the range and output signal in plain text whenever a transmitter is ordered.

Fitting an insert and avoiding common mistakes

Before exchanging an insert, isolate and cool the line, open the terminal head, disconnect the leads and withdraw the old insert. The new insert should be spring-loaded or seated against the bottom of the protection tube so the tip touches it; a gap increases response time and error (general practice). The terminal block carries the connection screws, and a transmitter can replace it, in which case ambient limits are reduced as stated for data sheets 70.7030 and 70.7010.

Do not mix sensor types: a Pt100 insert cannot be swapped for a Pt1000 without changing the instrument input, and thermocouple type L or K must match the compensating cable and controller setting. A 3 mm insert is slimmer and quicker but cannot be paired with two 3-wire Pt100 elements. For long inserts from 800 mm, only the mineral-insulated construction is acceptable. These inserts are a practical spares item for furnaces, boilers and process plants running JUMO form B probes, since keeping several lengths on the shelf avoids long outages.

Order information from the datasheet shows how the two families differ. The 909740/20 insert is mineral-insulated with a rigid first 50 mm and then a flexible part, which suits long or bent installation paths, and its standard range is -50 to +600 degC. The 909740/10 insert follows DIN 43762 for probes to DIN 43765/66 forms B and C, with -50 to +400 degC as standard. Tolerance class 1/3 DIN is offered besides class B and class A. The stock version 909740/10-402-1003-1-6-315/000 is a Pt100 insert of 6 mm diameter and 315 mm length.

Documents and quotation

The JUMO data sheet 90.9740 (dated 2009-11-12) can be downloaded below. Seven Star LLC supplies JUMO spare parts from Muscat; send the original probe type or the insert length, diameter, element and transmitter option and we will quote. Complete probes are listed under https://omansevenstar.com/product-category/sensors-transmitters/temperature/.