MTDC Penetrometer Evaluations at the Coeur d'Alene Nursery
MTDC evaluators completed side-by-side comparisons of the three hand-held electronic cone penetrometers at the Forest Service's Coeur d'Alene, ID, nursery in late September 2004. These comparisons looked first at how consistently each piece of equipment recorded soil strength and depth, then at the functionality, simplicity, operability, software, hardware, and output of each penetrometer. MTDC evaluators also compared hand-held electronic cone penetrometers with two mechanical penetrometers: the Compact-O-Gauge and a dynamic cone penetrometer. MTDC does not specifically endorse any of the equipment tested and did not test all hand-held electronic cone penetrometers that are available.
The primary goal was to evaluate how well each penetrometer recorded soil strength. MTDC purchased two units, the Rimik CP40 and the Spectrum Field Scout SC–900. The Eijkelkamp Penetrologger was borrowed from Soilmoisture Equipment Corp.
Models, Specifications, and Prices
Table 1 shows the specifications and costs of the three hand-held electronic cone penetrometers tested by MTDC.
| CP40 | Penetrologger | Field Scout SC–900 | ||
|---|---|---|---|---|
| Manufacturer | Agridry Rimik PTY LTD | Eijkelkamp Agrisearch Equipment | Spectrum Technologies, Inc. | |
| Units displayed | Metric only | Metric only | Metric or English | |
| Depth range | 0–600 mm (24 in) | 0–800 mm (32 in) | 0–450 mm (18 in) | |
| Pressure range | 0–5,500 kPa (798 psi) | 0–10,000 kPa (1,450 psi) | 0–7,000 kPa (1,000 psi) | |
| Maximum force | 75 kg (165 lb) | 102 kg (225 lb) | 95 kg (210 lb) | |
| Datalogger capacity 772 without GPS, (measurements) | 2,047 | 500 | 772 without GPS, 579 with GPS | |
| Weight | 3.9 kg (8.6 lb) | 2.9 kg (6.39 lb) | 1.25 kg (2.75 lb) | |
| Resolution | Depth | 1 mm (0.04 in) | 10 mm (0.39 in) | 25 mm (1 in) |
| Pressure | 1 kPa (0.15 psi) | 1 kPa (0.15 psi) | 35 kPa (5 psi) | |
| Accuracy | Depth | ±1 mm (±0.04 in) | ±10 mm (± 0.39 in) | ±12.5 mm (± 0.5 in) |
| Pressure | ±2.24 kPa (±0.32 psi) | ±2.0 kPa (±0.29 psi) | ±103 kPa (±15 psi) | |
| GPS compatible? | Yes | No | Yes | |
| Speed alarm | Yes | Yes | No | |
| Power (batteries) | 6-V gel cell, rechargeable | (2) D-size, nickel-cadmium | (2) AA alkaline | |
| Display | Graphic LCD | Graphic LCD | 16 character, 2-line LCD | |
| Warranty | 6 mo | 1 yr | 1 yr | |
| Cost (as of 3/15/2005) | $5,100 (CP40II) | $5,200 | $1,495 | |
Each penetrometer was tested for consistency in recording soil strength and depth by probing the ground in seven locations about 300 mm apart, while maintaining the recommended probe insertion speed of 30 mm/s. Figures 6, 7, and 8 show the results from each of the three penetrometers. The top 100 mm of soil showed very little resistance because the soil had been cultivated to this depth. A hardpan layer is at a depth of 350 to 400 mm.
The Rimik CP40 results are the most consistent. The graph of the Eijkelkamp Penetrologger test looks a little erratic in the lower half of the soil profile. Results of the Spectrum Field Scout SC–900 appear smoother than those of the Eijkelkamp Penetrologger, but the variability widens below 200 mm. The depth range of the three tested units varies from 450 to 800 mm as shown in table 1.
Figure 6—Repetition testing of the Rimik CP40 shows the unit's
consistency in documenting soil strength at various depths. Even
though the runs were conducted about 300 mm from each other,
some variation in readings can be expected because of differences
in ground conditions, equipment tracks, and operator
inconsistency. The Rimik CP40 displays metric units.
Figure 7—Repetition testing of the Eijkelkamp Penetrologger.
The first 100 mm of soil was weak because of recent tillage
in the
test field. The Eijkelkamp Penetrologger displays metric units.
Figure 8—Repetition testing of the Spectrum Field
Scout SC–900. The SC–900 outputs English or metric units.
In this test, several flags were set in a line about 3 m apart at the Coeur d'Alene Nursery. One probe insertion was made within 300 mm of every flag using each instrument. Figures 9 and 10 show the results of two side-by-side comparisons. At each location, the overall trend in soil strength is consistent among the penetrometers. The Eijkelkamp Penetrologger appears to record slightly higher soil strengths than the other two instruments.
Because of its rocky compacted soils, the Coeur d'Alene Nursery was not the best testing ground for studying the consistency of penetrometer readings. It was a good testing ground to show typical conditions and difficulties that can be encountered in field conditions. Figure 11 shows that at a depth of about 350 mm the Eijkelkamp Penetrologger recorded higher soil strength than the graph can display. Typically, such readings occur when the probe hits a rock. Some areas of the nursery were so dry and compacted that the probe couldn't even be inserted into the ground.
Figure 9—In the side-by-side comparison test, all three
penetrometers were reasonably consistent.
Probes were about 300 mm from each other.
Figure 10—The results from this comparison test show
less consistency, probably because of variation in ground
conditions, equipment tracks, or operator inconsistency.
Figure 11—This test shows some variation between the three
units in the side-by-side test. The wild jump in soil strength
on the Eijkelkamp
Penetrologger was caused by a rock or
very hard object at a depth of about 350 mm.
