INCOME TAXES (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of income tax expense
Current taxes - Federal			$ (124,000)	$ 240,000
Current taxes - State			10,000	10,000
Current taxes - Foreign			49,000	(13,000)
Deferred taxes - Federal			176,000	(167,000)
Deferred taxes - State			239,000	10,000
Deferred taxes - Foreign			25,000	(45,000)
Income tax expense			375,000	35,000
Reconciliation of federal income taxes and reported income taxes
Statutory federal tax provision (benefit)			(704,000)	27,000
State income tax benefit			(117,000)	(32,000)
Effect of foreign operations			(88,000)	107,000
Uncertain tax positions				2,000
Income tax credits			(112,000)	(134,000)
Valuation allowance			1,011,000	49,000
Permanent differences			8,000	16,000
Loss of Section 199 due to carryback claim			46,000
Effects of tax reforms			280,000
Other			51,000
Income tax expense			375,000	35,000
Income (loss) from operations before income taxes
Domestic			(2,831,433)	486,425
Foreign			760,658	(407,651)
Income (Loss) before income taxes			(2,070,775)	78,774
Components of deferred tax assets (liabilities)
Allowance for uncollectable accounts	$ 49,000		49,000	317,000
Inventories reserve	198,000		198,000	242,000
Accrued vacation	194,000		194,000	362,000
Amortization	191,000		191,000	56,000
Stock-based compensation and equity appreciation rights	23,000		23,000	29,000
Net operating loss carryforwards	359,000		359,000	134,000
Tax credit carryforwards	613,000		613,000	242,000
Other	23,720		23,720	188,000
Deferred tax assets before valuation allowance	1,650,720		1,650,720	1,570,000
Valuation allowance	(1,146,000)		(1,146,000)	(135,000)
Deferred tax assets	504,720		504,720	1,435,000
Prepaid expenses	(165,000)		(165,000)	(323,000)
Property and equipment	(319,000)		(319,000)	(569,000)
Deferred tax liabilities	(484,000)		(484,000)	(892,000)
Net deferred tax assets	20,720		20,720	543,000
Valuation allowance on foreign assets	0		0
Changes in total gross unrecognized tax benefit liabilities, excluding accrued interest
Balance at the beginning of the period		$ 52,000	52,000	51,000
Additions based on tax positions related to the current year			22,000	15,000
Additions based on tax positions related to a prior year				5,000
Reductions based on tax positions related to a prior year				(6,000)
Statute of limitations			(22,000)	(13,000)
Balance at the end of the period	52,000		$ 52,000	$ 52,000
Effective corporate tax rate			34.00%
Estimated income tax provision due to impact of the Tax Act	280,000
Provisional amount of net deferred tax	223,000
Provisional amount of transition tax	57,000
Provisional transition tax rate (in percent)			8.00%
Federal
Operating loss carryforwards
Net operating loss carryforwards	948,000		$ 948,000
Federal | General business
Tax credit carryforwards
Tax credit carryforwards	404,000		404,000
Minnesota | State
Operating loss carryforwards
Net operating loss carryforwards	1,144,000		1,144,000
Minnesota | State | R&D
Tax credit carryforwards
Tax credit carryforwards	330,000		330,000
Iowa | State
Operating loss carryforwards
Net operating loss carryforwards	357,000		357,000
Montana | State
Operating loss carryforwards
Net operating loss carryforwards	21,000		21,000
Wisconsin | State
Operating loss carryforwards
Net operating loss carryforwards	$ 669,000		$ 669,000
Forecast
Changes in total gross unrecognized tax benefit liabilities, excluding accrued interest
Effective corporate tax rate		21.00%