A simple approach to calculate active power of electrosurgical units

Monteiro, André Luiz Regis; Grande, Karin Cristine; Faria, Rubens Alexandre de; Schneider Junior, Bertoldo

doi:10.1590/2446-4740.0776

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Research on Biomedical Engineering

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Original Articles • Res. Biomed. Eng. 32 (1) • Jan-Mar 2016 • https://doi.org/10.1590/2446-4740.0776 copy

A simple approach to calculate active power of electrosurgical units

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Introduction:

Despite of more than a hundred years of electrosurgery, only a few electrosurgical equipment manufacturers have developed methods to regulate the active power delivered to the patient, usually around an arbitrary setpoint. In fact, no manufacturer has a method to measure the active power actually delivered to the load. Measuring the delivered power and computing it fast enough so as to avoid injury to the organic tissue is challenging. If voltage and current signals can be sampled in time and discretized in the frequency domain, a simple and very fast multiplication process can be used to determine the active power.

Methods

This paper presents an approach for measuring active power at the output power stage of electrosurgical units with mathematical shortcuts based on a simple multiplication procedure of discretized variables – frequency domain vectors – obtained through Discrete Fourier Transform (DFT) applied on time-sampled voltage and current vectors.

Results

Comparative results between simulations and a practical experiment are presented – all being in accordance with the requirements of the applicable industry standards.

Conclusion

An analysis is presented comparing the active power analytically obtained through well-known voltage and current signals against a computational methodology based on vector manipulation using DFT only for time-to-frequency domain transformation. The greatest advantage of this method is to determine the active power of noisy and phased out signals with neither complex DFT or ordinary transform methodologies nor sophisticated computing techniques such as convolution. All results presented errors substantially lower than the thresholds defined by the applicable standards.

Keywords:
Active power; Power measurement; Electrosurgery; FFT-computing; DFT

Zero-padding
Number of zeros	9000	19000	29000	39000	49000	59000	69000	79000	89000	99000
Active Power [W] (signal with noise)	28.72	28.74	28.77	28.78	28.75	28.78	28.69	28.79	28.75	28.71
	28.75	28.72	28.80	28.81	28.63	28.70	28.76	28.70	28.73	28.72
	28.77	28.76	28.79	28.73	28.78	28.73	28.74	28.74	28.75	28.71
	28.71	28.78	28.75	28.74	28.78	28.77	28.74	28.72	28.73	28.74
	28.71	28.74	28.71	28.75	28.77	28.71	28.75	28.72	28.73	28.82
	28.78	28.73	28.74	28.71	28.78	28.75	28.77	28.73	28.74	28.80
	28.80	28.76	28.76	28.76	28.69	28.70	28.76	28.77	28.68	28.72
	28.78	28.77	28.65	28.76	28.74	28.74	28.74	28.74	28.80	28.74
	28.78	28.72	28.74	28.71	28.78	28.73	28.72	28.69	28.74	28.71
	28.74	28.81	28.69	28.78	28.77	28.77	28.68	28.77	28.79	28.79
Average [W]	28.75	28.75	28.74	28.75	28.75	28.74	28.74	28.74	28.75	28.75
Average Result [W]					28.75
Expected Power [W]					27.00
Relative error					6.48%

Time Sampling	SNR_voltage	SNR_current	Active Power	Expected Active Power	Relative Error
(s)	(dB)	(dB)	(W)	(W)	(%)
1	22.62	22.83	28.82	27.00	6.76
10	22.62	22.83	28.83		6.78
20	22.62	22.83	28.84		6.80
60	22.63	22.83	28.83		6.79
1	28.65	28.86	27.84	27.00	3.10
10	28.64	28.85	27.83		3.09
20	28.64	28.85	27.83		3.08
60	28.64	28.85	27.83		3.09
1	42.63	42.83	27.15	27.00	0.57
10	42.63	42.83	27.15		0.57
20	42.62	42.83	27.15		0.57
60	42.62	42.83	27.15		0.57

Sequence	Sampled File (txt)	Power [W]	Sequence	Sampled File (txt)	Power [W]
1	23	30.46	23	47	32.96
2	24	30.54	24	48	32.48
3	26	30.15	25	49	32.90
4	27	30.17	26	51	63.96
5	28	30.61	27	52	64.22
6	29	29.99	28	53	61.47
7	30	30.40	29	54	63.11
8	31	30.18	30	55	60.46
9	32	30.40	31	56	26.17
10	33	30.04	32	57	25.46
11	34	30.04	33	58	24.67
12	35	29.11	34	59	29.42
13	36	29.59	35	60	10.04
14	37	29.56	36	61	10.54
15	39	28.99	37	62	9.95
16	40	28.99	38	64	10.82
17	41	29.91	39	65	13.50
18	42	33.39	40	66	11.95
19	43	32.22	41	67	4.92
20	44	32.58	42	68	9.64
21	45	32.46	43	69	11.33
22	46	33.27

Experiment Number	Media	Quantity	Duration (s)	Remark
22 to 41	Chayote	14	5
	Chayote	6	15
42 to 50	Chayote	9	20
51 to 55	Chayote	5	20	High Power
56 to 59	Swine flesh	4	5	Medium Power (some carbonization observed)
60 to 69	Swine flesh	10	20

Sociedade Brasileira de Engenharia Biomédica Centro de Tecnologia, bloco H, sala 327 - Cidade Universitária, 21941-914 Rio de Janeiro RJ Brasil, Tel./Fax: (55 21)2562-8591 - Rio de Janeiro - RJ - Brazil
E-mail: rbe@rbejournal.org

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[1] *e-mail: andre.regis13@gmail.com