Wood chips reaching a boiler or a dryer carry different amounts of water: a different batch, a different species, a different time in storage. The HGT-A transmitter measures the water content as it happens, straight in the material stream, and delivers the result as a 4-20 mA signal. The boiler or dryer controller therefore works on a figure from this moment, not on a sample taken before the shift. The measurement needs no sampling and no operator.
The transmitter is supplied as a ready calibrated system with the standard sensor, that is with the calibration for wood chips already stored in the device.
The transmitter is mounted in a screw conveyor or in a feed chute. The manufacturer states one construction condition outright: the wall thickness at the mounting point must not exceed 12 mm. The mounting surface has to be flat and the material has to press constantly against the face of the sensor, because the repeatability of the reading depends on it. The transmitter measures by the conductance method, that is the electrical conductivity of the material at the face of the sensor. Where the chips pass loosely and without pressure, the reading stops being repeatable.
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| Article number | 14236 | 12234 | ||||||
| Measuring range | 10 to 50 % water content | 10 to 60 % water content | ||||||
| Equivalent in wood moisture | up to 100 % | up to 150 % | ||||||
| Operating temperature | +5 to +40 °C | +5 to +85 °C | ||||||
| Analogue temperature output | option - art. no. 12327 | standard, 4-20 mA for +5 to +85 °C | ||||||
| Display with a keypad | option - art. no. 12426 | not among the accessories |
The mounting place decides the choice. The HGT-A is enough where the chips are already pre-dried and close to ambient temperature. The extended version is made for wetter and warmer material, directly behind a dryer for instance, and has the temperature output as standard.
Both quantities describe the same water, but they relate it to something different, so the same batch of chips carries two different numbers.
That is why 50 % water content is 100 % wood moisture, and 60 % water content is 150 % wood moisture. The HGT transmitters report the water content.
The result leaves the transmitter as a 4-20 mA current, that is in the form every boiler, dryer or processing line controller accepts. The water content output is scaled from 0 to 80 %. A second 4-20 mA output carries the material temperature: standard in the extended version, added as art. no. 12327 to the HGT-A. Where the reading is to be visible on the spot as well, a display with a keypad can be ordered in the HGT-A housing (art. no. 12426).
Advantages
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| Article number | 14236 | 12234 | ||||||
| Measuring range | 10 to 50 % water content (100 % wood moisture) | 10 to 60 % water content (150 % wood moisture) | ||||||
| Calibration accuracy against the reference material | ±5 % | ±5 % | ||||||
| Temperature compensation | automatic | automatic | ||||||
| Operating temperature | +5 to +40 °C | +5 to +85 °C | ||||||
| Temperature measuring range | -10 to +70 °C | +5 to +85 °C | ||||||
| Measuring method | conductance | conductance | ||||||
| Analogue output for the water content | 4-20 mA, scaled 0 to 80 % | 4-20 mA, scaled 0 to 80 % | ||||||
| Analogue output for the temperature | option - art. no. 12327, range -10 to +70 °C | 4-20 mA, range +5 to +85 °C | ||||||
| Power supply | 24 VDC (18 to 29 VDC) | 24 VDC (18 to 29 VDC) | ||||||
| Current consumption | 90 mA (without outputs and display) | 90 mA (without outputs and display) | ||||||
| Permissible load resistance | below 500 Ω | below 500 Ω | ||||||
| Protection rating | IP 54 | IP 54 | ||||||
| Dimensions | 188 × 88 × 77 mm | 188 × 88 × 77 mm | ||||||
| Weight | 744 g (without the cable) | 744 g (without the cable) | ||||||
| Wall thickness at the mounting point | up to 12 mm | up to 12 mm |
The scope of delivery is the same for both versions.
Checking the readings with the test blockTest block art. no. 12308 is used to check both transmitters, the HGT-A and the HGT-A extended. It makes it possible to check in moments whether the instrument reads as it did on the day of calibration, and to do so over the whole measuring range. The manufacturer gives the dimensions as 55 × 55 × 45 mm and the weight as 96 g; instructions come with the block. |
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Both systems measure the water content of wood chips continuously, but they are built differently. The HGT-A is a single instrument: the sensor and the electronics share one housing, it is mounted straight in the conveyor wall, and it comes factory calibrated for wood chips to an accuracy of ±5 %. The humimeter BLO is an analysing unit to which a separate external probe is chosen: it therefore covers a wider range of materials and reaches an accuracy of ±2.5 %, but it requires the probe to be selected and room for the unit itself.
The remaining biomass instruments are gathered in the bioenergy moisture meters category.
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