Non-contact system for measuring tillage depth

Computers and Electronics in Agriculture, 7 (1992) 133-147 Elsevier Science Publishers B.V., Amsterdam

133

Non-contact system for measuring tillage depth M. Yasin, R.D. Grisso and G.M. Lackas BiologicalSystems Engineering Department, Universityof Nebraska-Lincoln, USA (Accepted 31 July 1991)

ABSTRACT Yasin, M., Grisso,R.D. and Lackas,G.M., 1992. Non-contactsystemfor measuringsystemfor tillage depth. Comput. Electron. Agric., 7: 133-147. A microprocessor-basednon-contactultrasonicsensor for tillage depth was evaluated.The sensor was tested on concrete, grass, wheat stubble, lightlydisked wheat stubble (semi-stubble) and disked surfaces.The grass surfacegave a highervariationwhen comparedto results from measurementson the concretesurface.Largecoefficientsof variation were observedwhile operatingin standingstubble. Thus, the sensors did not provide sufficientaccuracywhen operatingin stubble conditions.The sensor performed well in a disked field and a pulled-typeimplementgave more consistent results comparedto that of a mountedfieldcultivator.

INTRODUCTION The effective control o f working depth o f tillage and seeding equipment is important for weed kill, i m p r o v e d seed germination and reduced energy consumption. Tillage depth has a remarkable influence on implement draft. Increasing the working depth o f an i m p l e m e n t increases all force components, wheel slip a n d fuel consumption ( G a r n e r et al., 1987). Wolf et al. (1981) determined that the draft per subsoiler shank increased from 2.52 to 6.20 kN as subsoiling depth increased from 0.28 to 0.44 m. Clark et al. ( 1981 ) stated that the soil depth had a p r o f o u n d effect on the draft o f sweep. Evans et al. (1984) reported that for each configuration o f a tillage tool there was a depth at which specific draft reached a m i n i m u m value. Spoor and G o d w i n (1978) found a critical working depth for all rigid tines below which compaction occurred and specific resistance increased. Bloome et al. (1983) said that accurate m e t h o d s for measuring implement working depth were essential in the draft studies. The tillage depth has been Correspondence to: R.D. Grisso, BiologicalSystemsEngineeringDepartment, University of Nebraska, L.W. Chase Hall, Lincoln, NE 68583-0726, USA. Published as Paper No. 9564 Journal Series, Agricultural Research Division, University of Nebraska, Lincoln, NE, USA.

0168-1699/92/$05.00 © 1992 ElsevierScience Publishers B.V. All rights reserved.

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difficult to measure accurately and measurement methods are affected by soil surface smoothness, trash cover and speed (Kydd et al., 1984). Mechanical height control systems such as gage wheels, skids and multiple trailing fingers are a common part of many types of agricultural machinery. Rehkugler (1970) used multiple trailing fingers to analyze dynamic behavior of an automatic combine header height control. Suggs and Abrams (1972) realized the shortcomings of conventional height control systems when they were used on rotary cutting devices. They suggested modification of a system to use hydraulic cylinders to control the height mechanism. Reidenbach et al. (1979) expanded the concept to control a header on a sugarcane harvester. Ruff et al. (1977) tested multiple trailing fingers on a sugarcane harvester to control cutting height. Clayton and Eiland (1977) investigated a sugarcane cutting height controller which used a pneumatic tire located behind the cutters to sense changes in the ground profile. Kaminski and Zoerb (1965) and Pask et al. (1973) used an electro-mechanical system which consisted of micro-switches and mechanical sensors for automatic control of cutterbar height. The ground contacting elements of the systems were subjected to excessive wear and damage during turning. In agricultural applications, ultrasonic techniques have been widely used for non-contact sensing. Warner and Harries (1972) used an ultrasonic sensor in a tractor guidance system. The system performed well on a test track, but difficulties were encountered in an agricultural environment due to inadequate reflection of ultrasound by the soil. Paulson and Strelioff (1974) used ultrasonic sensing to determine the height of a cultivator frame above the ground surface with an accuracy of 0.6 m m at a ground speed of 2.7 m]s. Bailey et al. (1974) utilized ultrasonics in an automatic controller to control the end of a loading boom of a potato harvester and significantly reduced bruising of the potatoes. O'Sullivan (1986) tested the ultrasonic sensor over various types of targets and reported that the transducer was suitable for numerous applications of non-contact measurements. Coad (1980) and Searcy et al. (1985 ) reported that ultrasonic sensors were useful for measuring relative ground height and stubble height. Gunderson et al. ( 1981 ) tested three tillage depth measuring systems: ultrasonic, ski and ski-wheel. The test results were linear and repeatable with tillage depth. However, they concluded that the ultrasonic system had the advantage of being a non-contact sensor with no moving parts and more reliable as a depth measurement system. They suggested the use of ultrasonic sensors into an electronic monitoring systems for drills and seeders to sense and control seeding rate and depth. Thornley et al. (1985) utilized an ultrasonic device to detect the top of a crop and an electro-mechanical system to locate the cutterbar height. They reported that the mechanical components of the systems were subjected to wear and damage and the detection of thin crops was unreliable.

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Leonard and Maki (1990) employed an ultrasonic sensor to detect cutter bar height and a microprocessor to process sensor data and control solenoid hydraulic valves. They reported the accuracy of the sensor output was independent of implement speed, but was dependent on the terrain type and sensor to target distance. False signals from dense green vegetation produced some false echoes. The objective of this study was to evaluate a non-contact measuring system for tillage depth. Ultrasonic sensors were incorporated into the microprocessor based data acquisition system developed by Lackas et al. ( 1991 ). INSTRUMENTATION

Ultrasonic proximity sensor. The AGASTAT ~ ultrasonic proximity sensor (PLEBM1SQDLP, Electro Corporation, Sarsota, FL) was selected because 6fits analog output and the built-in microprocessor. The unit has a wide beam, high gain sensing capability suitable for less reflective targets and can operate with a range from 41 to 163 cm at a standard frequency of 62.5 kHz. The sensor was composed of three subunits, a transmitter, a receiver and a builtin microprocessor, all enclosed in a single module 117 m m × 49 m m × 45 mm. The analog model uses 12-V DC input voltage and gives 4-20 mA current sinking output at 275 f~ maximum load impedance. A 650 m m 2 flat sound reflecting surface normal to the sensing axis provides a platform to return signal for sensing distance up to 163 cm. The transmitter sends which is echoed offthe reflecting object and received by the same module. Once received, the signal is amplified and filtered. The elapsed time for the signal to travel t o t h e object and return is related to the distance travelled. A built-in 8-bit microprocessor not only senses the target, but determines the position and tracks the target movement as the distance between the target and sensor changes. A 4-20 mA current loop output provides a signal base.d on the sensor distance. Temperature influences sensor signal. As the temperature deviates the apparent distance is adjusted about 0.2% per °C. A temperature compensation reference target (TCRT) provides a reference point that is a fixed distance from the sensor. Knowing this reference distance the sensor can compensate for variations in temperature. With a good reflective surface and temperature compensation, the accuracy of the output signal is estimated to be within 2% of the current loop valve. The uniformity of the reflecting surface directly affects signal strength, the smoother the soil surface the stronger the reflected signal (Coad, 1980). Wave ~Mention of trade and company names are for the benefit of the reader and do not infer endorsement or preferential treatment o f t h e products by the University of Nebraska.

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scattering from an irregular surface causes part of the reflected echo to be received and the remainder is lost. The noise, field dust and tilting of an ultrasonic sensor do not interfere with the sensor output, unless extreme tilting ( > 10 deg) is experienced.

Input conditioner card. A portable microprocessor-based data acquisition system developed by Lackas et al. ( 1991 ) was used for monitoring and recording of the target position (tillage depth). The system consisted of a laptop computer, a Daytronic Model 10KU analog/digital ( A / D ) signal conditioning unit (Daytronic Corp., Miamisburg, OH), a three-point hitch dynamometer and a fifth-wheel ground speed sensor used for tillage energy requirements research. The analog output signals of the ultrasonic sensors were fed to the Daytronic for digitizing and processing. A 4-20 mA input conditioner card (Model 10A61-2 dual input) was used. The conditioner card accepts independent current signal from each ultrasonic sensor. Since, the conditioner card did not have capability of providing excitation, an external 12-V DC power source was used to supply power to the sensors. Software developed by Lackas et al. ( 1991 ) was modified for collecting and storing ultrasonic sensors data. A calibration routine for the sensors was also added to the data acquisition software.

Sensor mounting. To protect the sensor from dust, rain and stubble, the sensor was fitted into a PVC pipe 78 m m inside diameter and 23 cm in length. The sensor was fixed in the pipe with its longitudinal axis collinear with the longitudinal axis of the pipe. The sensor outlet was 76 m m above the open end of the pipe (Fig. 1 ). The top end ofthe pipe was capped. The temperature compensation reference target (TCRT) for the ultrasonic sensor extended outside the PVC pipe. The beam angle of the sensor was 8 deg on all sides of the central beam width of 38 ram. However, the reflective properties of the targets can affect the apparent beam width. The inner diameter of the PVC pipe and the distance from the sensor outlet to pipe opening was selected so that the interference of the sound beam was minimized. The mounting unit was attached to the implement frame, mounted vertically above the center line of the rear tractor tire. This location gave a fairly uniform and hard reflecting surface with a minimal standing stubble. The height of the sensor above the ground surface was adjustable. An ultrasonic sensor was used on each side of the tillage implement to obtain accurate readings during field operations.

Sensor calibration. A two-point dead weight calibration method was used to calibrate the sensors. The slope factor and zero offset of the sensors were stored

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in the A / D unit's EPROM. These two calibration constants defined the indicated height as a linear function of current. The ultrasonic sensors were m o u n t e d on the tillage implement at heights within the operating range of the sensors. The tillage implement was parked on a fairly uniform and level surface. The implement was lowered down to the ground, with all the soil-engaging shanks resting on the ground surface. The implement was considered to be at the zero position. The calibration routine was activated. The heights of the sensors were manually measured and assumed to be the zero-working depth (Ho) of the implement (Fig. 2). The sensor was then moved down to a new position on the mounting unit without adjusting the implement. The new sensor height was again manually measured at the lowered position (HT). The height difference (d) and the zero working depth height were used by the calibration routine. After completing the calibration, the sensors were moved back to the zero working depth (Ho) position. EXPERIMENTAL PROCEDURE

Preliminary evaluation of the ultrasonic depth measuring system was conducted on the University of Nebraska Tractor Test Track and a grassy field. The sensors were m o u n t e d on a sensor support cart. The cart was equipped with a magnetic pickup device for speed measurement. The sensors were calibrated separately for each surface condition as recommended by Tompkins et al. (1988). Tests were conducted at various speeds and sensor heights above the grass and concrete surfaces. The cart was pushed at 4.8, 6.4, 8.0, 9.7 and 11.3 k m / h. The sensors were mounted at heights of 48, 52, 74 and 79 cm above the grass and concrete surfaces. The field study was conducted during August 1990 at the University of Nebraska Roger's Memorial Farm. The variables were operating speed, sen-

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sor height above ground, ground surface cover and type of tillage implement. The implements used in the tests were a tillage reference implement (TRI) and a field cultivator. The TRI was a tool bar 247 cm in width and 178 cm in length, equipped with two chisel shanks and two small V-blade sweeps. A common 25-tine field cultivator was also used. The statistical procedure used for the study was the split-split plot design in randomized complete block. Two separate experiments were conducted in a disked and an untilled fields. Three field speeds, three sensor target heights and two ground surface cover (wheat stubble and semi-stubble) were used in the first experiment. Thus, the total numbers of treatment combinations were 108 for six replications. The speeds 4.8, 6.4 and 9.7 k m / h and the sensor target heights 72, 79 and 87 cm were selected. The speeds, sensor target heights and ground covers were assigned randomly to the mainplots, subplots and sub-subplots, respectively. The ground cover was considered more important in this experiment and was placed in the sub-subplot. The wheat stubble height in the field ranged from 15 to 30 cm. The semi-stubble conditions were those existing after one pass of a disk. The sensors were mounted on the TRI for this experiment. The second experiment was done in the field that was disked twice and allowed to settle for 15 days. The test factors were speed, sensor target height and type of implement. The same three speeds were used. Three sensor target heights 87, 84 and 79 cm and two implements (TRI and field cultivator) with three replications gave 54 treatment combinations. The treatments were randomized within the mainplots, subplots and sub-subplots. The speeds, sensor target heights and implements were placed in the mainplots, subplots and subsubplots, respectively. The manually measured depth was measured for a given depth, while the implement was stationary. The computed depths were recorded while the implement was moving. Twenty data points for each of the two sensors, each point an average of three observations, were collected from each experimental unit (21.3 m by 4 m). RESULTS AND DISCUSSION

Preliminarystudy Performance ofthe ultrasonic sensors on a concrete surface at different sensor heights are illustrated in Figs. 3 and 4. The computed depth was plotted against the travel speed. The average computed depths for sensor height of 74 cm were 20.0, 21.6 and 20.5 cm at travel speeds of 8.0, 9.7 and 11.3 km/h, respectively (Fig. 3 ). The average computed depths were 0.5%, 3.5% and 3.0% higher for increasing travel speeds than the manually depth of 19.9 cm. The average computed depth at the sensor height of 79 cm were 3.0%, 1.0% and 3.0% higher with increasing travel speed than the manually measured depth

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Speed (kin/h) Fig. 4. Sensor performanceon tractortest track at sensorheights of 46 cm (H,) and 51 cm (H2) and at operating depths of 45 cm (MD,) and 41 cm (MD2). o f 10 cm. The standard deviation (SD), coefficient of variation ( c v ) and 95% confidence interval (cz) for the computer depth are listed in Table 1. The sensor height o f 79 cm gave a wider cz and higher c v , however in both cases the manually measured depths fell inside the confidence intervals. The computed depths at the lower sensor heights and at the higher travel speeds are shown in Fig. 4. The average computed depths at the sensor height o f 51 cm were 1.47% and 0.98% higher than the manually measured depth o f 40.9 cm at 11.3 and 12.9 k m / h travel speeds. The results at the lower sensor height gave the lowest c v and the narrowest cz (Table 1 ). The sensor height

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NON-CONTACTSYSTEMFORMEASURINGTILLAGEDEPTH TABLEI

Computed depth means, standard deviation, coefficient of variation, confidence interval and measured depths at four sensor heights on Tractor Test Track Sensor height Hr (cm)

Travel speed S (km/h)

Mean computed depth (cm)

Standard deviation SD (cm)

95% confidence interval (cm-cm)

Coefficient of variation cv (%)

Manually measured depth (cm)

79 79 79

8.0 9.7 11.3

10.3 10.1 10.3

0.33 0.24 0.34

9.6-11.0 9.7-11.6 9.6-11.0

3.2 2.33 3.3

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74 74 74

8.0 9.7 11.3

20.0 20.6 20.5

0.39 0.25 0.30

19.3-20.9 20.0-21.0 19.9-21. I

1.94 1.21 1.47

20 20a 20

51 51

11.3 12.9

41.5 41.3

0.28 0.40

40.9-42.1 40.5-42.2

0.66 0.97

41 41

46 46

11.3 12.9

47.8 51.2

4.36 6.29

38.9-56.9 38.0-64.5

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aOutside the 95% confidence interval. bLarger than 10% cv.

of 46 cm exhibited a higher variation (Fig. 4). The average computed depths were 5.5% and 13% higher than the manually measured depth of 45.3 cm at 11.3 and 12.9 k m / h travel speeds. A higher c v of 9.11 and 12.3 percent at 11.3 and 12.9 k m / h , respectively were determined at this sensor, height. The higher variation was due to the lower sensor height close to its m i n i m u m target height range. The sensor heights within the range recommended by the manufacturer had the least variation. In some cases at higher travel speeds, a slightly higher variation was observed. The sensor height of 51 cm gave the best results even at the higher speeds. The computed depths were 0.5-3.5% higher than the manually measured depths. Nine of the ten treatments gave c v s lower than 10%. The m i n i m u m and m a x i m u m cxs for all the treatments were 1.0 and 1.7 cm, excluding for the treatments at a sensor height of 46 cm. The sensor performance on a grass surface at the sensor heights of 52 and 67 cm is shown in Fig. 5. The average computed depths were 9.8%, 0.75%, 4.3% and 5.3% higher than the manually measured depth of 39.6 cm at 4.8, 6.4, 8.0 and 9.7 k m / h travel speeds, respectively. The-average computed depths for 67 cm sensor height were 13.2%, 8.0% and 48.4% higher than the manually measured depth of 25 cm at 6.4, 8.0 and 9.7 k m / h travel speeds, respectively. The computed depth means, so, c v and 95% cI are given in Table 2. All the treatments gave CVs lower than 10%. The m i n i m u m and m a x i m u m

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Speed (km/h) Fig. 5. Sensor performance on a grass surface at sensor heights o f 52 cm (H~) and 67 cm (H2) and at operating depths of 40 cm (MD~) and 25 cm (MD2). TABLE 2 Computed depth means, standard deviation, coefficient of variation, confidence interval and measured depths at two sensor heights on a grass surface Sensor height Hr (cm)

Travel speed S (km/h)

Mean computed depth (cm)

Standard deviation SD (cm)

95% confidence interval (cm-cm)

Coefficient of variation cv (%)

Manually measured depth (cm)

52 52 52 52

4.8 6.4 8.0 9.7

43.5 39.3 41.3 41.7

1.95 1.04 2.48 1.35

39.5-47.5 37.0-41.5 36.0-46.6 38.9-44.4

4.45 2.65 5.99 3.23

40 40 40 40

67 67 67

6.4 8.0 9.7

28.3 27.0 37.1

1.13 0.58 1.46

25.8-30.7 25.5-28.5 33.4-40.9

4.0 2.17 3.94

25 a 25a 25a

"Outside the 95% confidence interval.

cIs were 3.0 and 10.6 cm, respectively. Three of seven treatments had confidence intervals that.did not contain the manually measured depth. The grass surface tests demonstrated a larger variation as compared to the concrete surface results. On the grass surface there was a higher probability that the transducers sensed the ground at some spots, while at others it sensed the grass blades. Thus, the sensor output had a higher variability and it was further affected by the varying height of the grass.

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Field study-stubble field The analysis of variance (ANOVA) for the implement depth values in the wheat stubble field showed a highly significant difference ( P = 0 . 0 1 ) in average computed depths due to the treatments. Highly significant differences in average computed depths were found due to sensor height and ground cover. The speed did not significantly influence the computed depth. The interaction effect o f sensor height by ground cover gave a highly significant difference in computed depth. Similar results were reported by Leonard and Maki (1990). The other two factors and higher interaction effects were not significant (Table 3). The linear contrasts for sensor heights and ground covers were highly significant. This explains why the implement depth for the stubble and semi-stubble conditions were different. Likewise, the averaged computed depths for the three sensor heights were also different. Figure 6 demonstrates the sensor performance in the wheat stubble field at three sensor heights and two ground covers. The data points in Fig. 6 were averaged from both sensors. The results showed a high c v ranging from 14.1% to 25.3% for all the treatments considered. The average depths at the sensor height of 71 cm for the stubble and semistubble field tests were 15.2 and 14.6 cm as compared to the manually measured depth of 20.3 cm. The cI's for the depths ranged from 9.1 to 21.2 cm with a 20.2% c v for the stubble tests and from 10.4 to 18.7 cm with a 14.4% c v for the semi-stubble tests. All the treatments gave cvs higher than 10% and m i n i m u m and m a x i m u m cI's were 5.5 and 14.1 cm, respectively. The m i n i m u m cI's for the stubble and semi-stubble treatments were 7.8 and 5.5 cm, respectively. Since cI's are large (.>2.5 cm), the sensors are not sufficiently accurate for tillage depth control in stubble residue. The results for the sensor height of 79 cm were better than the results for the sensor heights of 87 and 72 cm. The tests for semi-stubble field gave a narrower cI for the implement depths at all the sensor heights, but showed a TABLE3 Analysis of variance results for the implement depth values for the stubble field tests (R2=0.87) Source of variation

Degree of freedom

F value

P value

Travel Speed (S) Sensor Height (Hr) Ground Cover (G) Replication (R)

2 2 1 5 4 2 2 4

1.83 82.61 54.28 7.90 0.50 0.90 7.54 0.99

0.1689 0.0001 0.0001 0.0001 0.7111 0.3972 0.0012 0.4186

SXHr S×G HrXG S×Hr×G

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Fig. 6. Sensor performance in stubble field at sensor heightsof 87 cm (Ht), 79 cm (H2) and 71 cm (H3), with stubble and semi-stubbleand at operating depths of 5 cm (MOt), 13 cm (MD2) and 20 cm (MD3). slightly higher c v than to the tests for the stubble field. The surface roughness due to clods and freshly tilled soil in the semi-stubble field probably contributed to higher cv. The sensor output for the stubble and semi-stubble tests were not found sufficiently accurate. The inaccuracy could be due to false echoes produced from stubble, green vegetation and surface roughness. The residue was less likely to be perpendicular to the signal than the ground surface and hence gave a scattered echoes. The variation was further increased by the lateral m o v e m e n t and bouncing of the implement over the rough field.

FieM study-disked field Highly significant differences (Table 4) in average computed depth were observed due to the treatments in the disked field. The interactions were not significant. The linear contrasts for the sensor heights and the types of implement were highly significant. The sensor results in the disked field at three sensor heights and two implements are plotted in Fig. 7. Treatments at the sensor heights of 84 and 79 cm gave a c v lower than 10%. The m i n i m u m and m a x i m u m cI's for all the treatments were 1.2 and 7.4 cm, respectively. The m i n i m u m cI'S for the TRI and field cultivator treatments were 1.2 and 1.9 cm, respectively. The average computed depths for the field cultivator at all three sensor heights were higher than the corresponding depths for the TRI. A higher c v for the computed depths was observed while operating the field cultivator. The higher variation could be attributed to the fact that the field cultivator was a m o u n t e d type implement and was more prone to the tractor rolling and

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TABLE 4 Analysis of variance results for the implement depth values for the disked field tests (R 2= 0.96) Source of variation

Degree of freedom

F value

P value

Travel Speed (S) Sensor Height (Hx) Implement (T) Replication (R)

2 2 1 2 4 2 2 4

1.89 289.36 38.36 0.44 1.78 0.08 3.18 0.04

0.1732 0.0001 0.0001 0.6517 0.1665 0.9273 0.0597 0.9962

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Speed (km/h) Fig. 7. Sensor performance in disked field at sensor heights of 87 cm (Hi), 84 cm (H2) and 79 cm (H3), with TRI and field cultivator and at operating depths of 5 cm (MD~), 7.6 (MD2) and 13 c m (MD3).

pitching during the field operation. The manually measured depths for all the treatments fell inside the c£s, except for the field cultivator at the sensor height of 79 cm. The results at the sensor height of 84 cm for the TRI treatments were found to be the best. From these results, the sensor performed satisfactorily in a disked field situation. CONCLUSIONS

Coefficients of variation less than 10% were observed in the computed depths tests on concrete and grass surfaces. The sensors on the grass surface gave a wider cI and a higher c v compared to the results for the concrete surface. The m i n i m u m cI's for the concrete and grass surfaces were 1.0 and 3.0 cm, respectively.

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M.YASINETAL.

The treatments for the stubble and semi-stubble experiment gave cv's higher than 10%. The minimum cI's for the stubble and semi-stubble treatments were 8.1 and 5.1 cm, respectively. The sensor is not sufficiently accurate when operating in residue covered conditions. The treatments for the disked field experiment gave cv's lower than 10%. The minimum cI's for the. TRI and field cultivator treatments were 1.2 and 1.9 cm, respectively. The sensor performed satisfactorily in the disked field. From all the treatments 28 of 53 responses had a c v less than 10% and 40 o f 53 treatments contained manually measured depth with in cI.

REFERENCES Bailey, E.M., Johnson, L.F., Rathbone, D.E. and Rolser, H.J., 1974. A potato harvester loading boom controller. In: IFAC Syrup. Automatic Control for Agriculture, 18-20 June, Saskatoon, Sask., Canada. Bloome, P.D., Batchelder, D.G., Khalilian, A. and Riethmuller, G.P., 1983. Effects of speed on draft of tillage implements in Oklahoma soils. ASAE Pap. 83-1032, 12 pp. Clark, S.J., Oni, K.C. and Johnson, W.H., 1981. Effect of sweep design parameters on draft. ASAE Pap. 81-1531, 30 pp. Clayton, J.E. and Eiland, B.R., 1977. Annual report of USDA sugarcane research laboratory. Belle Glade, FL, pp. 70-73. Coad, C.A., 1980. Microprocessor-based ultrasonic height controller for sugarcane harvesters. MS thesis, Texas A&M University, College Station, TX, 85 pp. Evans, D.E., Johnson, C.E. and Schafer, R.L., 1984. Tillage tools: how arrangement affects draft. Agric. Eng., 65: 18-24. Garner, T.H., Reynolds, W.R., Musen, H.L., Miles, G.E., Davis, J.W., Wolf, D. and Peiper, U.M., 1987. Energy requirement for subsoiling coastal plain soils. Trans. ASAE, 30: 343349. Gunderson, D.G., Kirk, T.G., Wilson, J.N. and Dyck, F.B., 1981. A comparison of ultrasonic, ski and ski-wheel systems for tillage depth measurement. ASAE Pap. 81-1602, 21 pp. Kaminski, T.L. and Zoerb, G.C., 1965. Automatic header-height control for grain crops. Trans. ASAE, 8: 284-287. Kydd, H.D., Frehlich, G.E. and Boyden, A.R., 1984. Tillage power requirements in Western Canada. ASAE Pap. 84-1027, 18 pp. Lackas, G.M., Grisso, R.D., Yasin, M. and Bashford, L.L., 1991. Portable data acquisition system for measuring energy requirements of soil-engaging implements. Comput. Electron. Agric., 5: 285-296. Leonard, J. and Maki, R., 1990. An automatic cutterbar height controller for grain harvesting machines. SAE Pap. 901560, Society of Automotive Engineers, Warrendale, PA, 6 pp. O'Sullivan, J.A., 1986. Evaluation of a Polaroid ultrasonic proximity transducer. J. Agric. Eng. Res., 34: 63-73. Pask, G.S., Wilson, J.N. and Zoerb, G.C., 1973. An automatic height-of-cut control system for windrowers. ASAE Pap. 73-155, 21 pp. Paulson, G.E. and Strelloff, W.P., 1974. An ultrasonic depth sensor. In: IFAC Symp. Automatic Control for Agriculture, 18-20 June, Saskatoon, Sask., Canada. Rehkugler, G.E., 1970. Dynamic analysis of automatic control ofcombine header height. Trans. ASAE, 13: 225-231.

NON-CONTACT SYSTF2,1 FOR MEASURING TILLAGE DEPTH

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Reidenbach, V.G., Coble, C.G., Dillon, R.C., Jr. and Ruff, J.H., 1979. Hydraulic pressure sensing for automatic depth control of sugarcane basecutter. ASAE Pap. 79-1570, 16 pp. Ruff, J.H., Feller, R., Dillon, R.C., Jr. and Coble, C.G., 1977. Potential sensors for automatic depth control of sugarcane basecutter blades. ASAE Pap. 77-1580, 18 pp. Searcy, S.W., Coble, C.G. and Coad, C.A., 1985. Stalk height estimation with ultrasonic. J. Am. Soc. Sugarcane Technol., 5: 27-33. Spoor, G. and Godwin, R.J., 1978. An experimental investigation into the deep loosening of soil by rigid tines. J. Agric. Eng. Res., 23: 243-258. Suggs, C.W. and Abrams, C.R., Jr., 1972. Automatic hydraulic height control mechanism for rotary cutting harvesting equipment. Trans. ASAE, 15: 428-432. Thornley, W.R., Park, H., Wiser, J.G. and Lundahl, E.C., 1985. Automatic sonar activated height control for a header. United States Patent No. 4507910. Tompkins, F.D., Hart, W.E., Freeland, R.S., Wilkerson, J.B. and Wilhelm, L.R., 1988. Com° parison of tractor ground speed measurement techniques. Trans. ASAE, 31: 369-374. Warner, M.G.R. and Harries, G.O., 1972. An ultrasonic guidance system for driverless tractors. J. Agric. Eng. Res., 17: 1-9. Wolf, D., Garner, T.H. and Davis, J.W., 1981. Tillage mechanical energy input and soil crop response. Trans. ASAE, 24: 1412-1419, 1425.