the OEM22 is a neat "flat pack" voltmeter module that can either be sub-panel mounted or used with the optional mb11 fixing bezel. the module is set up for 9 volt operation but can be adjusted for 5v use. a low bat annunciator is provided as standard (9vonly). the oem24l version comes complete with a green led backlight. all versions now co me with display hold feature. operating temperature 0 to 50 o c storage temperature -20 to 70 o c operating relative humidity 80% operating specification ordering information dimensions mm features revision 8 17/011/04 3.5 digit 12.7mm character height lcd 200mv full scale sensitivity automatic zeroing and polarity indication low battery indication (for 9v option only) 10 selectable annunciators easy to use decimal point selection display hold as standard OEM22 3.5 digit, 200mv lcd voltmeter oem24l 3.5 digit, 200mv lcd voltmeter with backlight mb11 optional mounting bezel description characteristic condition min typ max units supply voltage (vdd) 9 volts 5 volts 7 4.8 9 5 10 6 volts volts supply current (idd) 9 volts 5 volts 500 5 900 a ma full scale 199.9 mv input impedance 100 m ? ref voltage roh 9 volts 100 mv overload voltage 20 volts zero i/p reading 0 + 1 count accuracy at fsd 9 volts 5 volts + 1 + 1 + 2 + 4 counts counts resolution 100 v cmrr 70 db temp coefficient 100 150 ppm/ o c low battery ind. 9 volts only 6.75 7.25 7.75 v backlight volts oem24l 5 v backlight current at 5v - 40 60 ma electrical characteristics t a =25 o c ? pin description vdd positive supply terminal vss negative supply terminal for 9 volt mode only inhi inlo positive input terminal negative input terminal rfh rfl roh rol reference input high terminal reference input low terminal reference output high terminal reference output low terminal hold con. to vdd for display hold, to tst for normal. com analogue common tst connect to vdd to test all segments (except annunciators), for a few seconds only. (9v mode) also negative supply term inal for 5v supply. xbp for driving annunciators bp lcd back plane. d1, d2, d3 decimal point select. the decimal point will energize when these pins are tied to vdd. ab,b3,e3,g3, for use with ex ternal auto-ranging circuit. bat, o c, o f,~,m, , m, ? ,k ? ,v,a,hold annunciators. see user instructions. bat is auto turn on. turn it off in 5v mode by adjusting v2. lmp + backlight positive term inal (+5v dc) oem24l lmp - backlight negative terminal ( 0v dc) oem24l pin functions OEM22 and oem24l (backlit) 3.5 digit lcd digital voltmeters digital panel modules user guide
connection diagram basic configuration anders electronics plc bayham place, london nw1 oeu uk tel: +44 (0)20 7380 8167 fax: +44 (0 )20 7874 1908 h ttp:// www. anders.co.uk application circuits multi-range dc voltage measurement for multi-range, use a 2 pole, 4 way rotary switch. 1 pole for range select and the other to connect the appropriate decimal point to xbp. dc current measurement shunt resistance r s = v s ? it is important to note the power dissipation in the shunt and choose resistor rating accordingly p s = vs = i in r s ? examples 2 2 i in i in current r s p s 200ma 1 ? 0.04w 2a 0.1 ? 0.4w multi-range dc current measurement for multi-range, use a 2 pole, 5 way rotary switch. 1 pole for range select and the other to connect the appropriate decimal point to xbp. dc voltage ratio measurement to determine the ratio between two voltages apply the inputs as shown. displayed reading = v2 x 1000 over range occurs when v2 > 2 v1 v1 to achieve a zero display reading for a non-zero voltage input, apply the offset voltage between com and inlo. for a positive offset apply a positive signal to inlo w.r.t. com. apply the input signal between inhi and com . dc voltage offset the OEM22/24l is designed for 9/5v supply. incorrect supply polarity will destroy the module immediately. it is ready for general use when connected as in figure 1, for 9v supply. for 5v supply, the module must be calibrated before use as follows. connec t as in figure 2, apply 100mv to the inputs, from a calibrated source and adjust vr1 until the display reads 1000. the input range is 0-200mv. over-range is indicated by blanking the three least significant digits and displaying a "1" in the most significant digit. for 9v operation it is recommended to power from a 9v battery. the inputs are intended to float with respect to the supply but if they do not float they must be no closer than 1.5v from either vdd or vss (vdd-1.5v and vss+1.5v). see the circuits for non-floating inputs below. the low bat voltage can be set adjusting vr2 but it is not recommended to operate with a supply voltage below 7v. user instructions all annunciators are connected to bp for suppression purposes. to light up, cut t he trace between the selected annunciator pad and bp track and then link with solder the annunciator pad to the xbp pad next to it. for 5v operation, inlo must be connected to tst for non-floating inputs (as fig. 2) and to the analogue common pin com for floating inputs. the low bat annunciator needs to be turned of by adjusting vr2. where a single 5v supply is not suitable but you must connect your input signal ground to the module supply ground, then either of these two non-floating input ci rcuits can be used. note that the module is set in the 9v supply mode. non floating inputs (a) non floating i nputs (b) using the formulae choose resistors to ensure the analogue inputs are no closer than 1.5v from either vdd or vss (vdd-1.5v or vss+1.5v) dc voltage measurement to measure voltages greater than 200mv an attenuator is required. v in =v d x r1+r2 v d max. is 199.99mv examples v in display v d r1 r2 2v 1.999v 199.9mv 1m ? 110k ? 10v 1500rpm 150mv 1m ? 15k ? r2 the input impedance becomes r1+r2. choose accurate stable resistors. typically, r1=1m ?. 9m ? is a practical upper limit. revision 8 17/011/04
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