DWYER INSTRUMENTS, INC. Phone: 219/879-8000 www.dwyer-inst.com P.O. Box 373 • Michigan City, IN 46360, U.S.A. Fax: 219/872-9057 e-mail: info@dwyermail.com Our low cost Series 668 Differential Pressure Transmitter is capable ofmeasuring low pressures with a ±1% accuracy ideally suited for properbuilding pressurization and air flow control. Transmitters can withstandup to 10 psig overpressure with no damage to the unit. Variable capac-itance sensor design provides excellent sensitivity and long-term stabil-ity. Compact, lightweight design makes installation simple and easy.Units also feature reverse-polarity protection.INSTALLATIONMountingThe 668 Series is designed for mounting in either a switch box or byusing the two (2) holes that are provided on the housing. Optimum per-formance is obtained by isolating the instrument from vibration and pro-viding relatively clean, dry ambient air to the pressure ports. In mostcases, preferred installation is with the baseplate mounted vertically andlocated on a relatively flat surface in a junction box or attached to a near-by beam.CAUTION: The axis most sensitive to vibration is the one perpendicularto the mounting base. Avoid mounting with maximum vibration along theaxis.Pressure FittingTwo (2) 3/16˝ O.D. pressure fittings are supplied for pressure connec-tion with 1/4˝ push-on tubing. Both the positive (high) pressure port andthe reference (low) pressure port are located on the top face of the unit,labeled High and Low respectively. For best results (shortest responsetimes), 3/16˝ I.D. tubing is suggested for tubing lengths up to 100 feetlong, 1/4˝ I.D. for tubing lengths up to 300 feet, and 3/8˝ I.D. for tubinglengths up to 900 feet.Series 668 Differential Pressure TransmitterSpecifications - Installation and Operating InstructionsBulletin A-30-668SPECIFICATIONSService: Air and non-conductive gases. Accuracy:±1% of full scale (RSS) (includes non-linearity, hysteresis, and non-repeatability).Temperature Limits:Operating: 0 to 150°F (-18 to 65°C); Storage: -40to 185°F (-40 to 85°C).Pressure Limits:10 psig (0.7 kg/cm2).Compensated Temperature Range:0 to 150°F (-18 to 65°C).Thermal Effects: 0.033% FS/°F (0.018% FS/°C).Supply Voltage: 12-30 VDC.Output:4 to 20 mA, 2-wire.Zero and Span Adjust: ±1 mA, non-interactive.Response Time:<60 msec.Loop Resistance: 0-800 ohms.Electrical Connection: Terminal strip.Pressure Connection: 3/169 O.D. fitting for 1/49 I.D. tubing.Housing: Fire retardant glass filled polyester.Weight:3 oz (85 g).Agency Approvals: CE.Ø5/32 [3.97]MOUNTING HOLETYP 2 PLACES3-5/32[80.16] 3/8[9.53] 1-7/8[47.63] 6-32 SCREW W/TERMINAL WASHER 2-3/4[69.85] 1[25.40]3/16 [4.76]FITTING 3-1/2[88.90]1-41/64 [41.67]LOWHIGH _COM +EXCOUT®*Also available with optional conduit cover. To order add “C” to partnumber, i.e. 668C-1. Consult factory for additional information.Models & RangesModelNumber*668-1668-2668-3668-4Range0 to 0.25 in w.c.0 to 0.5 in w.c.0 to 1 in w.c.0 to 2.5 in w.cModelNumber*668-5668-6668-7668-8668-9Range0 to 5.0 in w.c.0 to 10 in w.c.0 to 25 in w.c0 to 50 in w.c.0 to 100 in w.c.Bi-Directional ModelsModelNumber*668-10668-11668-12668-13Range0 to ±0.1 in w.c.0 to ±0.25 in w.c.0 to ±0.5 in w.c.0 to ±1 in w.cModelNumber*668-14668-15668-16668-17668-18Range0 to ±2.5 in w.c.0 to ±5 in w.c.0 to ±10 in w.c0 to ±25 in w.c.0 to ±50 in w.c. D P w P F e ©Copyright 2018 Dwyer Instruments, Inc. FR# 443095-00 Rev. 3 DWYER INSTRUMENTS, INC. Phone: 219/879-8000 www.dwyer-inst.com P.O. Box 373 • Michigan City, IN 46360, U.S.A. Fax: 219/872-9057 e-mail: info@dwyermail.com ELECTRICAL CONNECTIONSThe Series 668 Differential Pressure Transmitter is a loop-powered 4 to20 mA current output unit. The current flows into +EXC. terminal andreturns back to the power supply through the -EXC. terminal. the powersupply must be a DC voltage source with a voltage range between 12and 30 VDC measured between terminal +EXC. and -EXC.The unit is calibrated at the factory using a 250 ohm load at 28 VDC.Notes: Minimum Supply Voltage (VDC) = 12 + 0.02 x (resistance of receiverplus line).Maximum Supply Voltage (VDC) = 30 + 0.004 x (resistance of receiverplus line).CALIBRATIONThe 668 series is factory calibrated and should require no field adjust-ment. However, both zero and span adjustments are provided.Whenever possible, any zero and/or span offsets should be corrected bysoftware adjustment in the user’s control system. Use the zero and spanadjustments on the 668 Series only if absolutely necessary. The 668series is calibrated in the vertical position at the factory. For use in otherorientations, position the unit and follow the zero adjustment procedurelisted below. Pressure ranges are fixed and cannot be changed in thefield.Zero AdjustmentWhile monitoring the current output with both pressure ports open toatmosphere, the zero may be adjusted. For unidirectional pressureranges, turn the zero adjustment screw until a reading of 4 mA (±0.15mA) is achieved.Span Adjustment (Complete the zero adjustment before settingspan)Span on full scale output adjustments should only be performed byusing an accurate pressure standard (electronic manometer, digitalpressure gage, etc.) with at least comparable accuracy to the 668 series(<±1% full scale). With full scale pressure applied to the high pressureport (reference port open to atmosphere) adjust span to achieve 20 mAoutput.Example 1: Unidirectional pressure range of 0 to 1˝ w.c. Apply 1.00˝ w.c.,adjust span to 20 mA.Notes: The input is reverse-voltage protected. The output is internallyprotected against damage is shorted to ground. Recheck all connectionsbefore applying power.MAINTENANCEAfter final installation of the Series 668 Differential Pressure Transmitter,no routine maintenance is required. A periodic check of system calibra-tion is recommended. These devices are not field repairable and shouldbe returned if recalibration or other service is required. Contact cus-tomer service to obtain an RGA number. Please include a clear descrip-tion of the problem plus any application information available.Next >