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Being a physicist I am wondering why it should be forbidden to pick the
legs of the sensor with metal tweezers whereas solderding (i.e. metallic
contacting to whatever) is officially discussed as viable. What
mechanism of harm is meant to be avoided by that prohibition?
Additionally I am wondering if metal tweezers picking is allowed if
I’d (contrary to the shown image) only grab the sensor at one leg -
which might be useful to suck away surplus heat from the active area in
the case of soldering the legs.
Additionally, is it allowed / suggested to pick the sensor with plastic
tweezers on both legs simultaneously? IMHO, this might induce rather
high local tensions by frictional electricity, potentially dangerous to
thin layer structures in the sensor, as it is specified for 12 V maximum
voltage?
Is there any request on the material properties of the suggested
handling gloves? They could as well produce large electric potentials
endangering the sensor. Or is it only to keep away body fat from the
active sensor area?
I’d like to use the sensor(s) for simultaneous measurement of hot water
vapour distrubutions in ovens. Is there a suggested readout method for
the bare sensors to respective capacitive measurement circuitry? I
intend to connect them to several inputs of a CAP1188 “touch sensor”
board, being programmed to serve as variable capacity readout, with
occasional recalibration in non-heated up state, or at least not
connected to the lead wires.
Concerning the “non-connected” state of the MK33-W: what is suggested to
couple it electro-mechanically to lead wires as near to the sensor as
possibly (and thus in the high temperature atmosphere, but with the lead
wires as basic capacity always present for recalibration) in a
detachable fashion?
The reason that the datasheet appears to recommend use of non-metallic tweezers for handling is unclear, but the risk of static discharge would seem the most likely, since the product appears to be based on use of a moisture-permeable thin film electrode. This would imply use of static dissipating “plastic” tweezers and gloves that of a static-dissipating, ESD-safe kind. Many nitrile gloves are sufficiently conductive for this purpose, though products with higher surface conductivity are also available for use when handling devices that are especially sensitive. The recommendation for use of gloves is most likely for chemical protection of the electrode material against the oils and salts present on the surface of one’s skin.
To query the raw sensor, a measurement instrument capable of resolving the sensor output to the desired precision, plus any parasitic elements added by the interconnections is needed. Devices designed for implementing touch-sensitive interfaces may be suitable, though there are also devices such as the AD5933 available which are designed for complex impedance measurement specifically, that may offer some advantages.
Regarding connectors, what sort of “oven” precisely it is that you speak of will influence the available options, since many plastics do not enjoy elevated temperatures. There are a variety of connector options available which are compatible with the ~26AWG (0.4mm) lead diameter of the sensor; products with gold finish may be preferable in the interest of limiting corrosion-related measurement influences. Regarding calibration, if possible I would suggest performing this function in systemic fashion if possible, to mitigate uncertainties associated with attempting to test the sensors and the system for interrogating them separately.
thanks a lot for your reply and explanations. So I’ll make sure to prevent ESD conditions even while handling the sensor rather with metallic tweezers, but with care, and wearing gloves against staining.
Regarding the capacitive readout the touch sensor chip (cap1188) is more than sensitive enough to detect the capacitance variations, provides auto-calibration of initial stray capacitance, and is stable in its readout for more than an hour after some pre-operation “burn-in” time before entering the real measurement phase. What bugs me more is the choice of sufficiently thin lead wires (must be lead through a rubber gasket) between sensor and readout chip that are not prone to false measurements even by an approximating hand.
The aspired oven will be one for food preparation, but will be operated in a clean mode without food and well below the given temperature limit. I’ll check for sensible sensor receptacles (up to 180 °C) that will have to be affixed to a (removable) test rack in the oven volume. Receptacle suggestions will be greatly appreciated!
Two-pin connectors rated to >180°C and designed for small wire sizes seem like a rare item. Assuming that you’re working in an experimental context rather than designing something for production, a possible solution may be to simply use common rectangular contact sets such as the 0561208428 and 0561198228 with some improvised housings made from high-temperature polymer stock.
There are some high-temperature, high-density connectors such as the micro-D series from ITT that might be useful in terms of making a pluggable connection between a test fixture with multiple sensors and an interrogation circuit outside the heated space. The exact nature of the connector systems you’re in need of isn’t quite clear, but perhaps these ideas will lead in a useful direction.
yes, you are right with the assumption of the purely experimental context, but at least aiming at an extended multi-sensor setup in case of positive experiences with the first sensors. And yes, indeed: my further investigations on high temperature connectors mostly caused shoulder shrugging, so your suggestions are highly welcome. I’ll talk to our prototyping guys if they could provide some custom polymer housing for the 0561208428 type sockets, with the potential to accommodate that into some easy-to-attach rigging. I’d expect to be able to push the round sensor pins immediately into the rectangular 0561208428 holes, right?
The micro-D sockets might be worth a thought, but I dislike their rather large occupied volume (and heat capacity) in the immediate vicinity of the tiny sensors, together with the lot of unused socket holes potentially creating condensation vessels during transient temperature/humidity states.
No, the idea would be to crimp the pin contacts onto the sensor leads, which then mate to the socket contacts mentioned. 26AWG is too thin for most push-in connector concepts to work well.
Again, these would not be suitable for engaging the sensors directly; if you wanted a hot zone connector for perhaps a dozen pre-wired sensors on a test fixture however, they might be an option.
There are also connectors designed for terminating magnet wire that might be useful. Some suited for 26AWG can be found here.
thanks for your valuable explanations and co-thinking effort! But I have to admit to have switched to I²C based sensors in the meantime as our measurement domain is just up to about 105 °C. The I²C humidity sensors offer simultaneous locally related temperature readouts and will obviously render more stable readings than managing a bunch of capacitive sensor chips via quite long primary cables to the sensing unit, and having to relate mechanically separate thermo-elements to them.
